#include <iostream>

 #include <cstdio>

 #include <string>

 #include <cstring>

 #include <map>

 #include <algorithm>

 #include <cmath>

 #define NV 101

 #define NE 202

 using namespace std;

 const int INF = <<;

 const double eps = 1e-;

 int ne, nv;

 int Rate[NV][NV];

 bool con[NV][NV];

 map<string, int> simap;

 bool Floyd()

 {

     for(int k = ; k < nv; ++k)

     for(int i = ; i < nv; ++i)

         if(Rate[i][k] < INF)

         for(int j = ; j < nv; ++j)

             if(Rate[k][j] < INF && Rate[i][j] > Rate[i][k] + Rate[k][j])

             Rate[i][j] = Rate[i][k] + Rate[k][j];

         for(int i = ; i < nv; ++i)

         for(int j = i; j < nv; ++j)

         {

             if(i != j && !con[i][j] && Rate[i][j] > )

             return false;

         }

     return true;

 }

 int main()

 {

     #ifndef ONLINE_JUDGE

     freopen("input.txt", "r", stdin);

     #endif

     while(cin >> nv >> ne)

     {

         for(int i=; i<nv; ++i)

         for(int j=i; j<nv; ++j)

         {

             Rate[i][j] = Rate[j][i] = INF;

             con[i][j] = con[j][i] = false;

         }

         for(int i=, u, v; i<ne; ++i)

         {

             cin >> u >> v;

             Rate[u][v] = Rate[v][u] = ;

             con[u][v] = con[v][u] = true;

         }

         if(Floyd()) printf("Yes\n");

         else printf("No\n");

     }

     return ;

 }