diff --git a/du4/program.c b/du4/program.c
index 9c9f236..e5d752c 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -23,7 +23,7 @@ int main(){
 
     float num2=strtof(start,&end);
 	start=end;
-    while((*start)<'0'||(*start)>'9'){
+    while((*start)<'0'||(*start)>'9'||(*start)=='-'){
         start++;
     }