/* -*- coding: utf-8 -*-
 *
 * 791.cc:  No.791 うし数列 - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

char s[128];

/* subroutines */

/* main */

int main() {
  scanf("%s", s);

  if (s[0] != '1') {
    puts("-1");
    return 0;
  }

  int k = 0;
  while (s[k + 1] == '3') k++;

  printf("%d\n", (k > 0 && s[k + 1] == '\0') ? k : -1);
  return 0;
}