diff --git a/du4/program.c b/du4/program.c
index f625f7e..ce9b0b2 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -48,6 +48,7 @@ double compare_percent(double a, double b, double eps)
 }
 
 int check(char *str){
+    int flag=0;
     char symb[5]="*-+/=";
     for(int i =0;i<strlen(str);i++){
         for(int k =0;k<5;k++){
@@ -57,8 +58,11 @@ int check(char *str){
                 }
             }
         }
+        if(str[i]=='='){
+            flag=1;
+        }
     }
-    return 1;
+    return flag==1?1:0;
 }