#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b) {
    int x = 1;
    a %= M;
    while (b) {
        if (b & 1) x = (x * a) % M; 
        a = (a * a) % M;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************




string a;

int consistency1(int n){
    int ans = n;

    unordered_set<int> st;
    for(int i=0; i<n; i++){
        st.insert(a[i]);
    }
    int k = st.size();

    unordered_map<int,int> mp;

    int s = 0, e = 0;
    while(e<n){
        mp[a[e]]++;
        if(mp.size() < k){
            e++;
        }
        else{

            while(s<=e && mp.size() >= k){
                ans = min(ans, e-s+1);
                mp[a[s]]--;
                if(mp[a[s]] == 0) mp.erase(a[s]);
                s++;
            }
            e++;
        }
    }
    

    return ans;    
}


int consistency2(int n){
    int ans = n;

    unordered_set<int> st;
    for(int i=0; i<n; i++){
        st.insert(a[i]);
    }
    int k = st.size();

    unordered_map<int,int> mp;

    int s = 0, e = 0;
    while(e<n){
        mp[a[e]]++;
        while(s<=e && mp.size() >= k){
            ans = min(ans, e-s+1);
            mp[a[s]]--;
            if(mp[a[s]] == 0) mp.erase(a[s]);
            s++;
        }
        e++;
    }
    

    return ans;    
}












int practice(int n){


    return 0;
}





void solve() {
    

    int n;
    cin>> n;

    cin >> a;
    
    
    cout << consistency2(n) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    // cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}