/in/foo.cc: In function 'int main()':
/in/foo.cc:55:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int k = i+1; k < yinshu.size(); k++)
                      ~~^~~~~~~~~~~~~~~
/in/foo.cc:61:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < yinshu.size(); i++)
                   ~~^~~~~~~~~~~~~~~
/in/foo.cc:43:13: warning: unused variable 'k' [-Wunused-variable]
   long long k = n;
             ^