diff --git a/Cargo.toml b/Cargo.toml
index 1fd5041..f936d74 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,3 +9,4 @@ edition = "2018"
 [dependencies]
 aoc-runner = "0.3.0"
 aoc-runner-derive = "0.3.0"
+nom = "6.0.1"
diff --git a/input/2020/day17.txt b/input/2020/day17.txt
new file mode 100644
index 0000000..8e1cf1a
--- /dev/null
+++ b/input/2020/day17.txt
@@ -0,0 +1,8 @@
+#.#.#.##
+.####..#
+#####.#.
+#####..#
+#....###
+###...##
+...#.#.#
+#.##..##
diff --git a/input/2020/day18.txt b/input/2020/day18.txt
new file mode 100644
index 0000000..ed81407
--- /dev/null
+++ b/input/2020/day18.txt
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+(4 * 4 + 5 + 9 * 9) + 2 + 2 + 9 * 3 * 5
+((9 + 7 + 6 + 8 + 8) + 4 + 4 * (2 * 5 * 8)) * 4 + 7 * 7 + 4 * (6 + 2 + 7 + 5 * 6)
+9 + 5 + 9 + 3
+4 * 6 * 5 + 3 + (7 * (2 + 5 + 2 * 5 + 9) + (2 + 9 + 8 * 9 + 3 * 3)) * 5
+(3 * 5 * (4 + 2 + 8 + 4 + 7) + 7 * 7) * (6 * 7 + 9 * 7 + 7 + 9)
diff --git a/src/day16.rs b/src/day16.rs
index 53481fd..d15fb5e 100644
--- a/src/day16.rs
+++ b/src/day16.rs
@@ -258,7 +258,7 @@ mod avx2 {
         let mut candidates = [_mm256_set1_epi32((1i32 << rules.len()) - 1); 4];
         let mut scratch_space = [_mm256_set1_epi32(1); 4];
         for line in nearby_tickets.split('\n') {
-            let scratch_slice = &mut * (&mut scratch_space as *mut _ as *mut [u32; 32]);
+            let scratch_slice = &mut *(&mut scratch_space as *mut _ as *mut [u32; 32]);
             for (field, scratch) in line.split(',').zip(scratch_slice.iter_mut()) {
                 let field = field.parse().unwrap();
                 *scratch = rule_eval.eval(field);
@@ -275,7 +275,7 @@ mod avx2 {
             }
         }
 
-        let candidates = &mut * (&mut candidates as *mut _ as *mut [u32; 32]);
+        let candidates = &mut *(&mut candidates as *mut _ as *mut [u32; 32]);
         let candidates = &mut candidates[..rules.len()];
         while candidates.iter().copied().any(|x| x.count_ones() > 1) {
             for idx in 0..candidates.len() {
diff --git a/src/day17.rs b/src/day17.rs
new file mode 100644
index 0000000..e34e8a1
--- /dev/null
+++ b/src/day17.rs
@@ -0,0 +1,6 @@
+use aoc_runner_derive::aoc;
+
+#[aoc(day17, part1)]
+fn solve_d17_p1(input: &str) -> usize {
+    42
+}
diff --git a/src/day18.rs b/src/day18.rs
new file mode 100644
index 0000000..3a59623
--- /dev/null
+++ b/src/day18.rs
@@ -0,0 +1,67 @@
+use aoc_runner_derive::aoc;
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::character::complete::{char, digit1, space0};
+use nom::combinator::map_res;
+use nom::multi::fold_many0;
+use nom::sequence::{delimited, pair};
+use nom::IResult;
+use std::str::FromStr;
+
+fn num(i: &str) -> IResult<&str, usize> {
+    map_res(delimited(space0, digit1, space0), FromStr::from_str)(i)
+}
+
+fn paren_expr(i: &str) -> IResult<&str, usize> {
+    delimited(space0, delimited(tag("("), expr, tag(")")), space0)(i)
+}
+
+fn num_or_paren_expr(i: &str) -> IResult<&str, usize> {
+    alt((num, paren_expr))(i)
+}
+
+fn expr(i: &str) -> IResult<&str, usize> {
+    let (i, lhs) = num_or_paren_expr(i)?;
+
+    fold_many0(
+        pair(
+            alt((char('+'), char('-'), char('*'), char('/'))),
+            num_or_paren_expr,
+        ),
+        lhs,
+        |lhs, (op, rhs)| match op {
+            '+' => lhs + rhs,
+            '-' => lhs - rhs,
+            '*' => lhs * rhs,
+            '/' => lhs * rhs,
+            _ => unreachable!("invalid op"),
+        },
+    )(i)
+}
+
+#[aoc(day18, part1)]
+fn solve_d18_p1(input: &str) -> usize {
+    input.split('\n').map(|line| expr(line).unwrap().1).sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_expr() {
+        assert_eq!(expr("2+2"), Ok(("", 4)));
+        assert_eq!(expr("1 + 2 * 3 + 4 * 5 + 6"), Ok(("", 71)));
+        assert_eq!(expr("1 + (2 * 3) + (4 * (5 + 6))"), Ok(("", 51)));
+        assert_eq!(expr("2 * 3 + (4 * 5)"), Ok(("", 26)));
+        assert_eq!(expr("5 + (8 * 3 + 9 + 3 * 4 * 3)"), Ok(("", 437)));
+        assert_eq!(
+            expr("5 * 9 * (7 * 3 * 3 + 9 * 3 + (8 + 6 * 4))"),
+            Ok(("", 12240))
+        );
+        assert_eq!(
+            expr("((2 + 4 * 9) * (6 + 9 * 8 + 6) + 6) + 2 + 4 * 2"),
+            Ok(("", 13632))
+        );
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 7cbb22b..841e47b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -6,6 +6,8 @@ pub mod day13;
 pub mod day14;
 pub mod day15;
 pub mod day16;
+pub mod day17;
+pub mod day18;
 pub mod day2;
 pub mod day3;
 pub mod day4;