/in/foo.cc: In function 'int main()':
/in/foo.cc:43:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < a.size(); i ++, time ++ ) res += a[i] * time;
                     ~~^~~~~~~~~~
/in/foo.cc:44:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < b.size(); i ++, time ++ ) res += b[i] * time;
                     ~~^~~~~~~~~~
/in/foo.cc:45:21: warning: format '%d' expects argument of type 'int', but argument 2 has type 'll {aka long long int}' [-Wformat=]
     printf("%d", res);
                     ^