/in/foo.cc: In function 'int main()':
/in/foo.cc:7:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<s[1].size();++i){
              ~^~~~~~~~~~~~
/in/foo.cc:12:7: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(k<=(s[1].size())/2)putchar('0');
      ~^~~~~~~~~~~~~~~~~