foo.cc: In function 'int main()':
foo.cc:23:11: warning: unused variable 'tmp' [-Wunused-variable]
 int a,b,c,tmp;
           ^~~
foo.cc:25:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d%d",&M,&N);
 ~~~~~^~~~~~~~~~~~~~
foo.cc:27:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d%d%d",&a,&b,&c);
 ~~~~~^~~~~~~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务