diff --git a/du4/program.c b/du4/program.c
index b1bf4b0..f625f7e 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -51,8 +51,10 @@ int check(char *str){
     char symb[5]="*-+/=";
     for(int i =0;i<strlen(str);i++){
         for(int k =0;k<5;k++){
-            if(str[i]==symb[k]&&str[i+1]==symb[k]){
-                return 0;
+            for(int j =0;j<5;j++){
+                if(str[i]==symb[j]&&str[i+1]==symb[k]){
+                    return 0;
+                }
             }
         }
     }