#include <iostream>
#include <sstream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <stack>
#include <memory>
#include <complex>
#include <numeric>
#include <cstdio>
#include <iomanip>

#define REP(i,m,n) for(int i=int(m);i<int(n);i++)
#define RREP(i,m,n) for(int i=int(n)-1;i>=int(m);--i)
#define EACH(i,c) for (auto &(i): c)
#define all(c) begin(c),end(c)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort(begin(c),end(c))
#define pb emplace_back
#define MP make_pair
#define SZ(a) int((a).size())

#ifdef LOCAL
#define DEBUG(s) cout << (s) << endl
#define dump(x)  cerr << #x << " = " << (x) << endl
#define BR cout << endl;
#else
#define DEBUG(s) do{}while(0)
#define dump(x) do{}while(0)
#define BR 
#endif
using namespace std;

using UI = unsigned int;
using UL = unsigned long;
using LL = long long int;
using ULL = unsigned long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VLL = vector<LL>;
using VVLL = vector<VLL>;
using VS = vector<string>;
using PII = pair<int,int>;
using VP = vector<PII>;

const int MAX = 500000, MS = 2;
const long long mod[] = {999999937LL, 1000000007LL}, base = 9973;

struct rolling_hash {
    int n;
    vector<long long> hs[MS], pw[MS];
    rolling_hash(){}
    rolling_hash(const string &s) {
        n = s.size();
        for (int i = 0; i < MS; i++) {
            hs[i].assign(n+1,0);
            pw[i].assign(n+1,0);
            hs[i][0] = 0;
            pw[i][0] = 1;
            for (int j = 0; j < n; j++) {
                pw[i][j+1] = pw[i][j]*base%mod[i];
                hs[i][j+1] = (hs[i][j]*base+s[j])%mod[i];
            }
        }
    }

    long long hash(int l, int r, int i) { return ((hs[i][r]-hs[i][l]*pw[i][r-l])%mod[i]+mod[i])%mod[i]; }

    bool match(int l1, int r1, int l2, int r2) {
        bool ret = 1;
        for (int i = 0; i < MS; i++) ret &= hash(l1,r1,i)==hash(l2,r2,i);
        return ret;
    }
};

bool solve(int &len, rolling_hash &rh, int &n, string &s) {
    //dump(len);
    /*
    REP(i,0,n-len+1) REP(j,i+len,n-len+1) {
        //cerr << i << ", " << j << endl;
        if (rh.match(i,i+len,j,j+len)) return true;
    }
    */
    vector<map<LL,int>> se(2);
    REP(i,0,n-len+1) {
        LL hash1 = rh.hash(i,i+len,0), hash2 = rh.hash(i,i+len,1);
        /*
        if (len == 3) {
            dump(hash1);
            dump(hash2);
        }
        */
        if (se[0].count(hash1) > 0 && se[1].count(hash2) > 0) {
            if (se[0][hash1] == se[1][hash2]) {
                if (se[0][hash1] + len <= i) return true;
                else continue;
            }
        }
        se[0].emplace(hash1,i);
        se[1].emplace(hash2,i);
    }
    return false;
};

int meguru_bin(rolling_hash &rh, int &n, string &s) {
    int ng = n + 1;
    int ok = -1;

    while (abs(ok - ng) > 1) {
        int mid = ng + (ok - ng) / 2;
        //cerr << ok << ", " << ng << ", " << mid << endl;
        if (solve(mid, rh, n, s)) ok = mid;
        else ng = mid;
    }

    return ok;
}

void solve() {
    int n;
    string s;
    cin >> n >> s;
    rolling_hash rh(s);
    cout << meguru_bin(rh,n,s) << endl;
}

int main() {
    solve();
    
    return 0;
}

Measured memory_bytes: 1024