#include <iostream>

#include <algorithm>
using namespace std;

int main() {
   int N;
   int A[210];    
   bool answer;
 int l, i=0, a[10];
    while(cin>>l){
        a[i] = l;
       
        i++;
    }
  sort(a, a+l);
     answer = true;
     
        for (int i = 0; i < 4; ++i) {
            if (a[i]+=1 == a[i+1]){answer = true;}else{ answer = false; break;}
        }


    
    
        if(answer==true) {cout << "yes" << endl; }else{cout <<"no" << endl; }

   

    
}