diff --git a/du4/program.c b/du4/program.c
index bea6389..3438acf 100644
--- a/du4/program.c
+++ b/du4/program.c
@@ -68,7 +68,7 @@ int main()
     sscanf(new_str,"%lf%c%lf%*[=]%lf",&first,&c,&second,&res);
     
     
-    if(c=='E'||first==-5||second==-5||res==-5){
+    if(c=='E'||first==-5||second==-5||res==-5||c!=43||c!=42||c!=45||c!=47){
         printf("CHYBA\n");
         return 0;
     }