#include <bits/stdc++.h>

using namespace std;

const int N = 1010, M = N << 2;
int e[M], h[N], idx, w[M], ne[M];
void add(int a, int b, int c = 0) {
    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
}
int n, m;
bool st[N];
int cnt;
void dfs(int u) {
    st[u] = 1;
    cnt++;
    for (int i = h[u]; ~i; i = ne[i]) {
        int v = e[i];
        if (!st[v]) dfs(v);
    }
}

int main() {
    memset(h, -1, sizeof h);
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        add(a, b);
    }

    dfs(1);

    if (cnt == n)
        printf("Yes\n");
    else
        printf("No\n");
    return 0;
}