Compilare: main.c: In function 'main': main.c:13:28: warning: unused variable 'r' [-Wunused-variable] unsigned long long a,b,r; ^ main.c:11:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("cmmdc.in","r",stdin); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:12:5: warning: ignoring return value of 'freopen', declared with attribute warn_unused_result [-Wunused-result] freopen("cmmdc.out","w",stdout); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:14:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result] scanf("%llu %llu",&a,&b); ^~~~~~~~~~~~~~~~~~~~~~~~