#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

#define INF (long long)(10e9+7)
#define REP(i,n) for(ll i = 0; i < n; i++)
#define REP1(i,n) for(ll i = 1; i <= n; i++)

int main(void)
{
    int a[5];
    REP(i, 4) cin >> a[i];
    sort(a,a+4);
    if(a[0]==a[1]-1 && a[1] == a[2]-1 && a[2] == a[3]-1) {
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }
}