beta.cpp

// NOTE: it is recommended to use this even if you don't understand the following code.

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

// input data
long long N;
vector<long long> V;

int main() {
//  uncomment the following lines if you want to read/write from files
	ifstream cin("input.txt");
	ofstream cout("output.txt");

    cin >> N;
    V.resize(N);
    for (long long i=0; i<N; i++)
        cin >> V[i];

    // insert your code here
    bool ans = false;
    bool doppio = false;
    long long num;
    
    sort(V.begin(), V.end());
    
    for (long long i=1; i<N; i++) {
    	if (V[i] == V[i-1]) {
    		if (!doppio) {
    			doppio = true;
    			num = V[i];
			} else {
				if (V[i] != num) {
					ans = true;
					break;
				}
			}
		}
	}
    
	if (ans) {
    	cout << "YES" << endl; // print the result
	} else {
		cout << "NO" << endl;
	}
    return 0;
}