#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T, class U> using Pa = pair<T, U>;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    vec<int> A(4);
    for(int i=0;i<4;i++) cin >> A[i];
    sort(A.begin(),A.end());
    bool ok = true;
    for(int i=0;i<3;i++) ok &= A[i]+1==A[i+1];
    cout << (ok? "Yes":"No") << "\n";
}