#include <bits/stdc++.h>
using namespace std;
int main() {
    string s; cin >> s;
    int n = s.size();
    vector<int> cnt(26, 0);
    for (int i = 0; i < n; i++) cnt[s[i]-'a']++;
    for (int i = 0; i < n; i++) if (cnt[s[i]-'a'] == 1) { cout << i << endl; return 0; }
    cout << -1 << endl;
    return 0;
}