/in/foo.cc: In function 'int main()':
/in/foo.cc:27:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j=0;j<s[i].size();j++) k=max(k,p[s[i][j]]);
                ~^~~~~~~~~~~~
/in/foo.cc:29:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j=0;j<s[i].size();j++) p[s[i][j]]=max(p[s[i][j]],f[i]);
                ~^~~~~~~~~~~~