/in/foo.cc: In function 'int sum(int, int, int)':
/in/foo.cc:5:24: error: expression cannot be used as a function
    5 |  int re=((m-n)/d+1)(m+n);
      |                        ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:12:21: error: expected primary-expression before ')' token
   12 |  while(cin>>n>>m>>d)){
      |                     ^