#include <bits/stdc++.h>

using namespace std;

vector<vector<int> > g, gr;
vector<char> used;
vector<int> order, component;

void dfs1(int v) {
    used[v] = true;
    for (size_t i = 0; i < g[v].size(); ++i)
        if (!used[g[v][i]])
            dfs1(g[v][i]);
    order.push_back(v);
}

void dfs2(int v) {
    used[v] = true;
    component.push_back(v);
    for (size_t i = 0; i < gr[v].size(); ++i)
        if (!used[gr[v][i]])
            dfs2(gr[v][i]);
}

int main() {
    int n, m, a, b, index_a, index_b, indexNot_a, indexNot_b;
    pair<int, int> kek;
    cin >> n >> m;
    n = n * 2;
    g.resize(n);
    gr.resize(n);

    vector<pair<int,int>> allVertexNotVertex;
    for (int i = 0; i < n; i+=2) {
        kek.first = i;
        kek.second = i + 1;
        allVertexNotVertex.push_back(kek);
    }

    for (int i = 0; i < m; i++) {
        cin >> a >> b;
        if (a < 0) {
            index_a = (-a * 2) - 1;
            indexNot_a = index_a - 1;
        } else {
            index_a = (a * 2) - 2;
            indexNot_a = index_a + 1;
        }
        if (b < 0) {
            index_b = (-b * 2) - 1;
            indexNot_b = index_b - 1;
        } else {
            index_b = (b * 2) - 2;
            indexNot_b = index_b + 1;
        }
        g[indexNot_a].push_back(index_b);
        gr[index_b].push_back(indexNot_a);
        g[indexNot_b].push_back(index_a);
        gr[index_a].push_back(indexNot_b);
    }

    used.assign(n, false);
    for (int i = 0; i < n; ++i)
        if (!used[i])
            dfs1(i);
    used.assign(n, false);
    for (int i = 0; i < n; ++i) {
        int v = order[n - 1 - i];
        if (!used[v]) {
            dfs2(v);
            sort(component.begin(), component.end());
            for (int j = 0; j < component.size() - 1; j++) {
                if (component[j + 1] - component[j] == 1) {
                    kek.first = component[j];
                    kek.second = component[j + 1];
                    auto result1 = find(allVertexNotVertex.begin(), allVertexNotVertex.end(), kek);
                    if (result1 != allVertexNotVertex.end()) {
                        cout << "YES";
                        return 0;
                    }
                    else
                        continue;
                }
            }
            component.clear();
        }
    }
    cout << "NO";

    /*
    vector<bool> core(2*n, 0);
    vector<vector<bool>> graph(2*n, core);

    for (int i = 0; i < m; i++) {
        cin >> a >> b;
        if (a < 0) {
            index_a = (-a * 2) - 1;
            indexNot_a = index_a - 1;
        }
        else {
            index_a = (a * 2) - 2;
            indexNot_a = index_a + 1;
        }
        if (b < 0) {
            index_b = (-b * 2) - 1;
            indexNot_b = index_b - 1;
        }
        else {
            index_b = (b * 2) - 2;
            indexNot_b = index_b + 1;
        }
        graph[indexNot_a][index_b] = 1;
        graph[indexNot_b][index_a] = 1;
    }

    for (int i = 0; i < 2*n; i++) {
        for (int j = 0; j < 2*n; j++) {
            cout << graph[i][j] << " ";
        }
        cout << endl;
    }
    */

    return 0;
}