#include <bits/stdc++.h>

using namespace std;

int main(){
  string S;
  cin >> S;
  for(int i = 1; i < S.size(); i++) {
    if(S[i] != '3') {
      cout << "-1\n";
      return 0;
    }
  }
  if(S.size() >= 2) cout << S.size() - 1 << endl;
  else cout << -1 << endl;
}