#include <bits/stdc++.h>

#define D 400007

using namespace std;
typedef long long ll;

vector <ll> a[D], ta[D], ts;
ll used[D], comp[D], ccount;

void topsort(ll v)
{
    used[v] = true;
    for (ll to : a[v])
        if (!used[to])
            topsort(to);
    ts.push_back(v);
}
void dfs(ll v)
{
    comp[v] = ccount;
    for (ll to : ta[v])
        if (!comp[to])
            dfs(to);
}

void add(ll v1, ll v2)
{
    a[v1].push_back(v2);
    ta[v2].push_back(v1);
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    ll n, m, x1, x2;
    while (cin >> n >> m)
    {
        for (ll i = 0; i < D; i++)
        {
            a[i].clear();
            ta[i].clear();
        }
        ts.clear();
        memset(used, 0, sizeof(used));
        memset(comp, 0, sizeof(comp));
        ccount = 0;

        for (ll i = 1; i <= m; i++)
        {
            cin >> x1 >> x2;
            if (x1 < 0 && x2 < 0)
            {
                x1 = -x1; x2 = -x2;
                add(x1, x2 + n);
                add(x2, x1 + n);
            }
            if (x1 > 0 && x2 > 0)
            {
                add(x1 + n, x2);
                add(x2 + n, x1);
            }
            if (x1 < 0 && x2 > 0)
            {
                x1 = -x1;
                add(x1, x2);
                add(x2 + n, x1 + n);
            }
            if (x1 > 0 && x2 < 0)
            {
                x2 = -x2;
                add(x1 + n, x2 + n);
                add(x2, x1);
            }
        }
        topsort(1);
        if (used[1 + n])
        {
            cout << "no" << endl, 0;
            continue;
        }

        for (ll i = 2; i <= n * 2; i++)
            if (!used[i])
                topsort(i);
        reverse(ts.begin(), ts.end());

        for (ll v : ts)
            if (!comp[v])
            {
                ccount++;
                dfs(v);
            }
        for (ll i = 1; i <= n; i++)
            if (comp[i] == comp[i + n])
            {
                cout << "no" << endl, 0;
                continue;
            }

        cout << "yes" << endl;
    }
    return 0;
}