#include <bits/stdc++.h>
using namespace std;
#define Rep(i,n) for(int i=0;i<(int)(n);i++)
#define For(i,n1,n2) for(int i=(int)(n1);i<(int)(n2);i++)
#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define RREP(i,n) for(ll i=((ll)(n)-1);i>=0;i--)
#define FOR(i,n1,n2) for(ll i=(ll)(n1);i<(ll)(n2);i++)
#define RFOR(i,n1,n2) for(ll i=((ll)(n1)-1);i>=(ll)(n2);i--)
#define all(a)  (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define oorret 0
#define oor(x) [&](){try{x;} catch(const out_of_range& oor){return oorret;} return x;}()
#define IOS cin.tie(0),ios::sync_with_stdio(false)
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
template<typename T1, typename T2> inline bool chmin(T1& a, T2 b) { if (a > b) { a = b; return 1; }return 0; }
template<typename T1, typename T2> inline bool chmax(T1& a, T2 b) { if (a < b) { a = b; return 1; }return 0; }
template<class Type>struct is_vector : std::false_type {};
template<class ValueType, class Alloc>struct is_vector<std::vector<ValueType, Alloc>> : std::true_type {};
template <typename T> inline ostream& operator << (ostream& out, const vector<T>& v) {
	if (v.empty())return out;
	constexpr bool is_vector_v = is_vector<T>::value;
	if (is_vector_v)for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? "\n" : "");
	else for (auto itr = v.begin(); itr != v.end();)out << (*itr), out << ((++itr != v.end()) ? " " : "");
	return out;
}
inline void put() {}
template<class T> inline void put(const T& first) { std::cout << first << "\n"; }
template<class T, class... N> inline void put(const T& first, const N& ... rest) { std::cout << first << " "; put(rest...); }
inline void putn() {}
template<class T, class... N> inline void putn(const T& first, const N& ... rest) { std::cout << first << "\n"; putn(rest...); }

class RollingHash {
private:
	const ull base;
	const vector<ull> mod;
	const int n;
public:
	RollingHash(const vector<ull>& mod, const ull& base) :mod(mod), base(base), n((int)mod.size()) {}
	bool contain(const string& s, const string& t) {//sのsubstringにtが存在するか
		return contain(s, t, 0, s.size());
	}
	bool contain(const string& s, const string& t, int l, int r) {//sの[l,r)にsubstringにtが存在するか
		int sl = (int)s.size(), tl = (int)t.size();
		chmin(r, sl);
		chmax(l, 0);
		int ran = r - l;
		if (ran < tl)return false;
		vector<ull> sh(n, 0), th(n, 0), p(n, 1);
		bool flag = true;
		for (int i = 0; i < n; ++i) {
			for (int j = l; j < l + tl; ++j) {
				sh[i] = sh[i] * base + s[j];
				if (sh[i] > mod[i])sh[i] %= mod[i];
				th[i] = th[i] * base + t[j-l];
				if (th[i] > mod[i])th[i] %= mod[i];
				p[i] *= base;
				if (p[i] > mod[i])p[i] %= mod[i];
			}
		}
		for (int i = 0; i < n; ++i) {
			if (th[i] != sh[i])flag = false;
		}
		if (flag) {
			return true;
		}
		for (int j = l + tl; j < r; ++j) {
			flag = true;
			for (int i = 0; i < n; ++i) {
				sh[i] = sh[i] * base + s[j];
				if (sh[i] < p[i] * s[j - tl]) {
					sh[i] += mod[i] * s[j - tl];
				}
				sh[i] -= p[i] * s[j - tl];
				if (sh[i] > mod[i])sh[i] %= mod[i];
			}
			for (int i = 0; i < n; ++i) {
				if (th[i] != sh[i])flag = false;
			}
			if (flag) {
				return true;
			}
		}
		return false;
	}
	vector<int> find(const string& s, const string& t) {
		return find(s, t, 0, s.size());
	}
	vector<int> find(const string& s, const string& t, int l, int r) {//sのsubstringがtである先頭のindexを返す
		int sl = (int)s.size(), tl = (int)t.size();
		vector<int> res;
		int ran = r - l;
		if (ran < tl)return res;
		vector<ull> sh(n, 0), th(n, 0), p(n, 1);
		bool flag = true;
		for (int i = 0; i < n; ++i) {
			for (int j = l; j < l + tl; ++j) {
				sh[i] = sh[i] * base + s[j];
				if (sh[i] > mod[i])sh[i] %= mod[i];
				th[i] = th[i] * base + t[j-l];
				if (th[i] > mod[i])th[i] %= mod[i];
				p[i] *= base;
				if (p[i] > mod[i])p[i] %= mod[i];
			}
		}
		for (int i = 0; i < n; ++i)if (th[i] != sh[i])flag = false;
		if (flag)res.push_back(0);
		for (int j = l + tl; j < r; ++j) {
			flag = true;
			for (int i = 0; i < n; ++i) {
				sh[i] = sh[i] * base + s[j];
				if (sh[i] < p[i] * s[j - tl]) {
					sh[i] += mod[i] * s[j - tl];
				}
				sh[i] -= p[i] * s[j - tl];
				if (sh[i] > mod[i])sh[i] %= mod[i];
			}
			for (int i = 0; i < n; ++i)if (th[i] != sh[i])flag = false;
			if (flag)res.push_back(j - tl + 1);
		}
		return res;
	}
};


int main() {
	IOS;
	int n;
	string s;
	cin >> n >> s;
	const vector<ull> mod = { 2000000011 };
	random_device rnd;
	mt19937 mt(rnd());
	const ull base = mt() + 1e5;
	using RH = RollingHash;
	RH r(mod, base);
	int lb = -1, ub = n+1;
	while (ub - lb > 1) {
		int mid = (ub + lb) / 2;
		bool flag = false;
		REP(i, n - mid) {
			string tmp;
			FOR(j, i, i + mid) {
				tmp += s[j];
			}
			if (r.contain(s, tmp, i + mid, n)) {
				flag = true;
				break;
			}
		}
		if (flag) {
			lb = mid;
		} else {
			ub = mid;
		}
	}
	put(lb);
	return 0;
}

Measured memory_bytes: 256