#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0; i<(n); ++i)
#define REP(i, d, n) for(int i=(d); i<(n); ++i)
#define all(v) v.begin(), v.end()
using ll = long long;
using P = pair<int, int>;

int main() {

    int a[4];
    cin >> a[0] >> a[1] >> a[2] >> a[3];

    sort(a, a+4);

    bool ok = true;
    REP(i, 1, 4){
        if(a[i-1] != a[i] - 1){
            ok = false;
            break;
        }
    }
    if(ok){
        cout << "Yes" << endl;
    }
    else{
        cout << "No" << endl;
    }



    return 0;
}