/*
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*/

#include <bits/stdc++.h>

// #include <iostream> // cout, endl, cin
// #include <string> // string, to_string, stoi
// #include <vector> // vector
// #include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
// #include <utility> // pair, make_pair
// #include <tuple> // tuple, make_tuple
// #include <cstdint> // int64_t, int*_t
// #include <cstdio> // printf
// #include <map> // map
// #include <queue> // queue, priority_queue
// #include <set> // set
// #include <stack> // stack
// #include <deque> // deque
// #include <unordered_map> // unordered_map
// #include <unordered_set> // unordered_set
// #include <bitset> // bitset
// #include <climits>
// #include <cmath>
// #include <iomanip>
// #include <functional>
// #include <numeric>
// #include <random>

using namespace std;
    
#define int long long
#define pb push_back
#define F first
#define S second
#define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define rep(i,n) FOR(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define ve vector
#define vi vector<int>
#define vp vector<pair<int,int>>
#define vvi vector<vector<int>>

template<typename T> using pq = priority_queue<T,vector<T>,greater<T>>; 
using ll = long long;
ll INF = LLONG_MAX / 4000 - 100;
ll mod = 1e9 + 7;
int dx[] = {-1,0,1,0}, dy[] = {0,1,0,-1};
vector<ll> prime;
    
class fact {
public:
    int fmod = 1e9+7;
    vector<int> fac, inv;
    fact (int n, int Mod = 1e9+7) {
        fmod = Mod;
        fac = vector<int>(n,0);
        inv = vector<int>(n,0);
        fac[0] = 1; for (int i = 1; i < n; i++) fac[i] = fac[i-1] * i % fmod;
        for (int i = 0;i < n;i++) inv[i] = fact::POW(fac[i],fmod-2);
    }
    ll nCr(ll n, ll r) {if(n < r) return 0; return (fac[n] * inv[r] % fmod) * inv[n-r] % fmod;}
    ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%fmod;}a = a * a%fmod; b >>= 1;}return c;}
    inline int operator [] (int i) {return fac[i];}
};
    
template <class T = ll> T in() {T x; cin >> x; return (x);}
void DEBUG(vector<int> a) {for(int i=0;i<a.size();i++)cout<<a[i]<<" ";cout<<endl;}
void EMP(int x) {cout<<"!!!"<<x<<"!!!"<<endl;}
ll GCD(ll a, ll b) {ll c; while (b != 0) {c = a % b; a = b; b = c;}return a;}
ll LCM(ll a, ll b) {return (a / GCD(a, b)) * (b / GCD(a, b)) * GCD(a, b);}
ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%mod;}a = a * a%mod; b >>= 1;}return c;}
void PRI(ll n) {bool a[n + 1LL]; for (int i = 0; i < n + 1LL; i++) {a[i] = 1LL;}for (int i = 2; i < n + 1LL; i++) {if (a[i]) {prime.pb(i); ll b = i; while (b <= n) {a[b] = 0; b += i;}}}}
template <typename T> T chmin(T& a, T b) {if(a>b)a=b;return a;}
template <typename T> T chmax(T& a, T b) {if(a<b)a=b;return b;}
bool isSqrt(ll a) {return pow(sqrt(a),2) == a ? 1 : 0;}
void YesNo(bool a) {if (a) cout << "Yes"; else cout << "No"; cout << endl;}
void yesno(bool a) {if (a) cout << "yes"; else cout << "no"; cout << endl;}
void YESNO(bool a) {if (a) cout << "YES"; else cout << "NO"; cout << endl;}
double dis(int x1, int x2, int y1, int y2) {
    return sqrt((double)abs(x1-x2)*(double)abs(x1-x2)+(double)abs(y1-y2)*(double)abs(y1-y2));
}

class RollingHash {
using ull=unsigned long long;
ull POW(ull a, ull b) { ull c = 1; while (b > 0) { if (b & 1) { c = a * c; }a = a * a; b >>= 1; }return c; }
public:
	vector<ull> hash[2],power[2];
	ull base[2], mod[2];
	RollingHash (string &s) {
		base[0] = 1000000007; base[1] = 999999937;
		mod[0] = 998244353, mod[1] = 1000000009;
		int sz = (int)s.size();
		for (int i=0; i<2; i++) {
			hash[i].assign(sz+1,0);
			power[i].assign(sz+1,0);
			power[i][0] = 1;
		}
		rep (i,sz) {
			for (int j=0; j<2; j++) {
				power[j][i+1] = power[j][i] * base[j] % mod[j];
				hash[j][i+1] = (hash[j][i] * base[j] + s[i]) % mod[j];
			}
		}
	}
	//半開区間!!!
	//abcde
	//hash[0]=0,hash[1]=a,hash[2]=ab,hash[3]=abc;
	//bcならget(1,3)
	pair<ull,ull> get(int l,int r) {
		ull h1 = hash[0][r] - (hash[0][l] * power[0][r - l] % mod[0]) + mod[0];
		ull h2 = hash[1][r] - (hash[1][l] * power[1][r - l] % mod[1]) + mod[1];
		h1 %= mod[0], h2 %= mod[1];
		return {h1, h2};
	}
};

bool solve() {
    vi cnt(26, 0);
    vi pos[26];
    int n; cin >> n;
    string s; cin >> s;
    vi rui[s.size()+1];
    rep (i, s.size()+1) rui[i] = vi(26);

    rep (i, s.size()) {
        cnt[s[i]-'a']++;
        pos[s[i]-'a'].pb(i);
        rep (j, 26) {
            rui[i+1][j] = rui[i][j];
        }
        rui[i+1][s[i]-'a']++;
    }
    bool fl = true;
    rep (i, 26) {
        if (cnt[i] > 1) fl = false;
    }
    if (fl) {
        cout << 0 << endl;
        exit(0);
    }
    RollingHash rh(s);

    int l = 1, r = n / 2 + 1;
    while (r - l > 1) {
        bool ok = false;
        int mid = (r + l) / 2;
        rep (i, n - 2*mid + 1) {
            auto ck = rh.get(i, i+mid);
            int start = rui[i+1][s[i]-'a'];
            FOR (J, start, cnt[s[i]-'a']) {
                if (pos[s[i]-'a'][J] < i + mid) continue;
                if (pos[s[i]-'a'][J] > n - mid) break;
                int j = pos[s[i]-'a'][J];
                if (rh.get(j, j+mid) == ck) {
                    ok = true;
                    break;
                }
            }
            if (ok) break;
        }
        if (ok) l = mid;
        else r = mid;
    }

    cout << l << endl;
}

signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}


Measured memory_bytes: 1792