#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
using ll = long long;
using namespace std;
const int INF = 1e9;

int main() {
    int A[4];
    rep(i, 4) cin >> A[i];
    sort(A, A + 4);

    bool flag = true;
    rep(i, 3) {
        if(A[i]!=A[i+1]-1)
            flag = false;
    }
    flag ? cout << "Yes" : cout << "No";
    cout << endl;

    return 0;
}