diff --git a/day1/day1/Cargo.toml b/day1/day1/Cargo.toml
index 4b25ec1..781048b 100644
--- a/day1/day1/Cargo.toml
+++ b/day1/day1/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [features]
-big = []
+big = ["u128"]
+u128 = []
 
 [dependencies]
diff --git a/day1/day1/src/main.rs b/day1/day1/src/main.rs
index 5b54227..fcf6d7f 100644
--- a/day1/day1/src/main.rs
+++ b/day1/day1/src/main.rs
@@ -11,27 +11,40 @@ use input::INPUT;
 #[cfg(not(feature="big"))] const TARGET: u64 = 2020;
 #[cfg(feature="big")] const TARGET: u64 = 99920044;
 
-// O(n^2)
+// O(n^2) ?
 fn main() {
-    let deficits: HashMap<u64, usize> = (0..)
-	.zip(INPUT.iter().copied())
-	.filter_map(|(i, x)| TARGET.checked_sub(x).map(|x| (x, i)))
+    // doesn't work on big input?
+    #[cfg(feature="u128")] 
+    let input: Box<[_]> = INPUT[..].iter().map(|&x| x as u128).collect();
+    #[cfg(feature="u128")] 
+    let target = TARGET as u128;
+    // ^ doesn't help..
+
+    #[cfg(not(feature="u128"))] 
+    let input = &INPUT[..];
+    #[cfg(not(feature="u128"))] 
+    let target = TARGET;
+    
+    let deficits: HashMap<_, usize> = (0..)
+	.zip(input.iter().copied())
+	.filter_map(|(i, x)| target.checked_sub(x).map(|x| (x, i)))
 	.collect();
 
-    //eprintln!("calculated deficits: {}", deficits.len());
-    for (i, ix) in (0..).zip(INPUT.iter().copied())
+    eprintln!("calculated deficits: {}", deficits.len());
+    for (i, ix) in (0..).zip(input.iter().copied())
     {
-	for jx in INPUT[i..].iter().copied().skip(1)
+	for jx in input[i..].iter().copied().skip(1)
 	{
-	    let sum = ix+jx;
-	    if let Some(&idx) = deficits.get(&sum)
-	    {
-		//eprintln!("solution found?");
-		println!("{}", if let Some(x) = INPUT[idx].checked_mul(ix).map(|x| x.checked_mul(jx)).flatten()
-			 { x } else { continue; });
-		return;
+	    if let Some(sum) = ix.checked_add(jx) {
+		if let Some(&idx) = deficits.get(&sum)
+		{
+		    eprintln!("solution found?");
+		    println!("{}", if let Some(x) = input[idx].checked_mul(ix).map(|x| x.checked_mul(jx)).flatten()
+			     { x } else { continue; });
+		    return;
+		}
 	    }
 	}
     }
-    //panic!("no solution");
+    panic!("no solution");
 }