#include"stdio.h"
#define max 1240
unsigned p[max][max/32];
unsigned pow[33];
int r[max][max];
int n , s;

void solve()
{
	int i , j , k , l , x , h;
	unsigned tmp;
	
	for(i = 0;i < n;i++)
	{
		for(j = 0;j < n;j++) 
		{
			if(!r[i][j] && i != j)
				for(k = 0;k < s;k++)
					if(p[i][k]&p[j][k])
					{
						tmp = p[i][k]&p[j][k];
						for(l = 0;l < 32;l++)
							if(tmp&pow[l])
							{
								x = 32*k+l;
								for(h = 0;h < n;h++)
									if(!r[h][i]&&!r[h][x]&&r[h][j])
									{
										puts("No");
										return;
									}
							}
					}
		}
	}
	puts("Yes");
}

int main()
{
	int i , m , a, b;

	scanf("%d%d",&n,&m);
	s = (n+31)/32;
	for(i = 1;i <= 32;i++)
		pow[i] = (unsigned)1 << i;
	for(i = 0;i < m;i ++)
	{
		scanf("%d %d",&a,&b);
		a--;b--;
		r[a][b] = 1;
		r[b][a] = 1;
		p[a][b/32] |= pow[b%32];
		p[b][a/32] |= pow[a%32];
	}
	solve();
	return 0;
}