diff --git a/src/day18.rs b/src/day18.rs
index c2e10d6..0d97ee8 100644
--- a/src/day18.rs
+++ b/src/day18.rs
@@ -4,7 +4,7 @@ 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::sequence::{delimited, preceded};
 use nom::IResult;
 use std::str::FromStr;
 
@@ -20,32 +20,18 @@ fn num_or_paren_expr(i: &str) -> IResult<&str, usize> {
     alt((num, paren_expr))(i)
 }
 
-fn add_or_sub(i: &str) -> IResult<&str, usize> {
+fn add_or_paren(i: &str) -> IResult<&str, usize> {
     let (i, lhs) = num_or_paren_expr(i)?;
 
-    fold_many0(
-        pair(alt((char('+'), char('-'))), num_or_paren_expr),
-        lhs,
-        |lhs, (op, rhs)| match op {
-            '+' => lhs + rhs,
-            '-' => lhs - rhs,
-            _ => unreachable!("invalid op"),
-        },
-    )(i)
+    fold_many0(preceded(char('+'), num_or_paren_expr), lhs, |lhs, rhs| {
+        lhs + rhs
+    })(i)
 }
 
 fn expr(i: &str) -> IResult<&str, usize> {
-    let (i, lhs) = add_or_sub(i)?;
+    let (i, lhs) = add_or_paren(i)?;
 
-    fold_many0(
-        pair(alt((char('*'), char('/'))), add_or_sub),
-        lhs,
-        |lhs, (op, rhs)| match op {
-            '*' => lhs * rhs,
-            '/' => lhs / rhs,
-            _ => unreachable!("invalid op"),
-        },
-    )(i)
+    fold_many0(preceded(char('*'), add_or_paren), lhs, |lhs, rhs| lhs * rhs)(i)
 }
 
 #[aoc(day18, part1)]