foo.cpp: In function 'int main()':
foo.cpp:5:15: error: 'scanf' was not declared in this scope
  scanf("%d",&n);
               ^
foo.cpp:18:19: error: 'printf' was not declared in this scope
  printf("%d\n",ans);
                   ^
foo.cpp:4:12: warning: unused variable 'm' [-Wunused-variable]
  int i,j,k,m,n;
            ^