#include<bits/stdc++.h>
#define REP(i,n) for(int i=0,i##_len=int(n);i<i##_len;++i)
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
#define All(x) (x).begin(),(x).end()
#define rAll(x) (x).rbegin(),(x).rend()
using namespace std;
using ll = long long;

int main(){
    int A[4];
    REP(i,4) cin>>A[i];
    sort(A,A+4);
    REP(i,3){
        if(A[i]+1!=A[i+1]){
            cout<<"No"<<endl;
            return 0;
        }
    }
    cout<<"Yes"<<endl;
}