#include"bits/stdc++.h"
#include"atcoder/all"
using namespace std;
using namespace atcoder;
#pragma GCC target("avx2")
#pragma GCC optimize("O2")
#pragma GCC optimize("unroll-loops")
using ll = long long;
using ld = long double;
#define rep(i,m,n) for(ll i=(ll)m;i<(ll)n;i++)
#define drep(i,m,n) for(ll i=m-1;i>=n;i--)
#define Endl endl
#define pr(i,j) make_pair(i,j) 
#define isin(x,l,r) (l<=x&&x<r)
#define chmin(a,b) a=min(a,b)
#define chmax(a,b) a=max(a,b)
#define srt(ar) sort(ar.begin(),ar.end())
#define rev(ar) reverse(ar.begin(),ar.end())
#define jge(f) cout<<(f?"Yes":"No")<<endl
const ll inf = 1e18;
const ld pi = 3.14159265358979;
using mint = modint998244353;
clock_t ST, FN;
int main() {
	ST = clock();
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	vector<ll>ar(4);
	rep(i, 0, 4)cin >> ar[i];
	srt(ar);
	rep(i, 0, 3) {
		if (ar[i] + 1 != ar[i + 1]) {
			cout << "No" << Endl;
			return 0;
		}
	}
	cout << "Yes" << endl;
}