//
// Created by Даниил Королёв on 31.10.2018.
//
#include <vector>;
#include <iostream>;
#include <cmath>;

using namespace std;

int getBit(int number, int shift) {
    return (number >> shift) % 2;
}

int invert(int number) {
    if (number == 0) return 1;
    else return 0;
}

int main() {
    int n, m;
    cin >> n >> m;
    int size = pow(2, n);
    int matrix[size][n];
    int pairs[2 * m];
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < n; j++) {
            matrix[i][j] = getBit(i, n - j - 1);
        }
    }
    for (int i = 0; i < 2 * m; i++) {
        cin >> pairs[i];
    }
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < 2 * m; j += 2) {
            int first = pairs[j];
            int second = pairs[j + 1];
            int firstBit = matrix[i][abs(first) - 1];
            int secondBit = matrix[i][abs(second) - 1];
            if (first < 0) {
                firstBit = invert(firstBit);
            }
            if (second < 0) {
                secondBit = invert(secondBit);
            }
            if (secondBit == 0 && firstBit == 0) {
                break;
            } else {
                if (j == 2 * (m - 1)) {
                    cout << "NO";
                    return 0;
                } else {
                    continue;
                }
            }
        }
    }
    cout << "YES";
    return 0;
}