#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);

    int a[4];
    rep(i,4) cin >> a[i];
    sort(a, a + 4);
    bool ng = false;
    rep(i,3) if(a[i+1] - a[i] != 1) ng = true;
    cout << (!ng ? "Yes" : "No") << endl;
}