/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:8:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(step == s.length()-1){
        ~~~~~^~~~~~~~~~~~~~~
/in/foo.cc:14:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if(step+i < s.length()){
            ~~~~~~~^~~~~~~~~~~~
/in/foo.cc:21:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if(step+3 < s.length()){
            ~~~~~~~^~~~~~~~~~~~