/*
*/

//#pragma comment(linker, "/STACK:16777216")
#include <fstream>
#include <iostream>
#include <string>
#include <complex>
#include <math.h>
#include <set>
#include <vector>
#include <map>
#include <queue>
#include <stdio.h>
#include <stack>
#include <algorithm>
#include <list>
#include <ctime>
#include <memory.h>
#include <ctime>

#define y0 sdkfaslhagaklsldk
#define y1 aasdfasdfasdf
#define yn askfhwqriuperikldjk
#define j1 assdgsdgasghsf
#define tm sdfjahlfasfh
#define lr asgasgash

#define eps 1e-9
//#define M_PI 3.141592653589793
#define bs 1000000007
#define bsize 256
#define right adsgasgadsg
#define free adsgasdg
#define MAGIC 47
#define count adsgasdgasdg

using namespace std;

int n,m,a,b;
bool ar[10050][10050];
int used[10050];
int visited;

void dfs(int v)
{
 used[v]=1;
 visited++;
 for (int i=1;i<=n;i++)
  if (ar[v][i]==1&&used[i]==0)
   dfs(i);
}

int main(){
//freopen("k.in","r",stdin);
//freopen("k.out","w",stdout);
//freopen("C:/input.txt","r",stdin);
//freopen("C:/output.txt","w",stdout);
ios_base::sync_with_stdio(0);
//cin.tie(0);

cin>>n>>m;
for (int i=0;i<m;i++)
{
 cin>>a>>b;
 ar[a][b]=ar[b][a]=1;
}
if (m!=n-1)
{
 cout<<"NO"<<endl;
 return 0;
}

dfs(1);
if (visited!=n)
cout<<"NO"<<endl;
else cout<<"YES"<<endl;

cin.get();cin.get();
return 0;}