#include <stdio.h>

int a[1001][1001];  
int visit[1001];  

void DFS(int m, int n) {
    visit[m] = 1;  
    for (int i = 1; i <= n; i++) {
        if (a[m][i] == 1 && visit[i] == 0) { 
            DFS(i, n); 
        }
    }
}
int main() {
    int u, b, c, d;
    while (scanf("%d %d", &u, &b) != EOF) {
        for (int i = 1; i <= u; i++) {
            visit[i] = 0;  
            for (int j = 1; j <= u; j++) {
                a[i][j] = 0;  
            }
        }
        for (int i = 1; i <= b; i++) {
            scanf("%d %d", &c, &d);
            a[c][d] = 1;  
            a[d][c] = 1;  
        }
        DFS(1, u);
        int flag = 1;
        for (int i = 1; i <= u; i++) {
            if (visit[i] == 0) {  
                flag = 0;
                printf("NO\n");
                break;  
            }
        }
        if (flag == 1) {
            printf("YES\n");
        }
    }
    return 0;
}