diff --git a/main.go b/main.go
index 01e6413..287307c 100644
--- a/main.go
+++ b/main.go
@@ -285,23 +285,20 @@ func (dm *DocumentManager) compareFiles(f1Number, f2Number int) (float64, error)
 	}
 
 	histogram := make(map[string]int)
-	for _, lines := range [][]string{f1, f2} {
-		for _, line := range lines {
-			// Skip blank lines, which can throw off the count.
-			if line == "" {
-				continue
-			}
+	for _, line := range f1 {
 			histogram[line]++
 		}
+	for _, line := range f2 {
+		histogram[line]--
 	}
 
-	var overlap int
+	var differences float64
 	for _, v := range histogram {
-		if v == 2 {
-			overlap++
-		}
+		differences += math.Abs(float64(v))
 	}
-	return float64(overlap) / float64(len(histogram)), nil
+
+	similarity := 1 - (differences / float64(len(f1)+len(f2)))
+	return similarity, nil
 }
 
 // Document stores a document ID and a list of associated files.