/in/foo.cc: In function 'int main()':
/in/foo.cc:16:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<s.size();i++)
          ~^~~~~~~~~
/in/foo.cc:6:29: warning: unused variable 'j' [-Wunused-variable]
  ll mod=998244353,ans=1,n,i,j,k;
                             ^