3

#include <bits/stdc++.h>
using namespace std;

void solve(){
    int n;
    string s;
    cin >> n >> s;
    int posa = -22, posb = -22, posc = -22, posd = -22;
    int ans = -1;
    for (int r = 0; r < n; r++){
        if (s[r] == 'a') posa = r;
        if (s[r] == 'b') posb = r;
        if (s[r] == 'c') posc = r;
        if (s[r] == 'd') posd = r;
        int l = min(min(posa, posb), min(posc, posd));
        int le = r - l;
        int len = le + 1;
        if (l != -22){
            if (ans == -1 || len < ans){
                ans = len;
            }
        }
    }
    cout << ans << endl;
}

int main(){
    ios::sync_with_stdio(NULL), cin.tie(0), cout.tie(0); // Оптимизация
    solve();
}