#include <bits/stdc++.h>

using namespace std;

int arr[1001] = {0};

int main() {
    int n, m;
    cin >> n >> m;
    bool flag = false;
    for (int i = 1; i <= m; i++) {
        int a;
        cin >> a;
        if (arr[a] == 0) arr[a] = 1;
        else {
            arr[a]++;
            cout << "yes" << endl;
            flag = true;
            break;
        }
    }
    if (!flag)cout << "no" << endl;
    return 0;
}