#include<bits/stdc++.h>
using namespace std;
using i64 = int_fast64_t;
#define rep(i, N) for(int (i) = 0; (i) < (N); (i)++)
#define all(v) (v).begin(), (v).end()
#define eb emplace_back

int main(){
    vector<int> S(4);
    rep(i, 4) cin >> S[i];
    sort(all(S));
    bool ok = true;
    for(int i = 1; i < 4; i++) ok &= (S[i] == S[i-1] + 1);
    if(ok) cout << "Yes" << endl;
    else cout << "No" << endl;
}