/in/foo.cc: In function 'void delete2min(std::__cxx11::string&)':
/in/foo.cc:26:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<str.length()-1;i++){
              ~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:43:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   if(pos==str.npos || pos>k) break;
          
/in/foo.cc:49:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  if(str.empty() || str.length()<=k){
                    ~~~~~~~~~~~~^~~