#define _LIBCPP_DEBUG 0
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
ll MOD = 1e9 + 7;



int main(void){

    vector<int> A(4);
    for (int i = 0; i < 4; ++i) {
        cin>>A[i];
    }

    sort(A.begin(), A.end());

    bool ok = true;
    for (int i = 1; i < 4; ++i) {
        if(A[i]!=A[i-1]+1) {
            ok = false;
            break;
        }
    }

    if(ok){
        cout<<"Yes"<<endl;
    }else{
        cout<<"No"<<endl;
    }

}