#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<math.h>
using namespace std;
#define N (1000000000+7)
#define INF 1e16
typedef long long ll;
typedef pair<int,int> P;



int main(void){
    int a[4];
    for(int i=0;i<4;i++)cin>>a[i];
    sort(a,a+4);
    for(int i=0;i<3;i++){
        if(a[i]+1!=a[i+1]){
            cout<<"No"<<endl;
            return 0;
        }
    }
    cout<<"Yes"<<endl;
    return 0;
}