#include<bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int) n; i++)
#define repb(i, n) for (int i = (int) n; i >= 0; i--)
#define reps(i, m, n) for (int i = (int) m; i < (int) n; i++)
#define repsb(i, m, n) for (int i = (int) m; i >= (int) n; i--)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
# define pb(a) push_back(a)
#define ll long long int
int dy[] = { 0, 0, 1, -1, 0 };
int dx[] = { 1, -1, 0, 0, 0 };
template < class T > bool chmax(T & a,const T & b) { if (a < b) { a = b; return 1; } return 0; }
template < class T > bool chmin(T & a,const T & b) { if (b < a) { a = b; return 1; } return 0; }
//vector<vector<int>> vec(n_rows, vector<int>(n_cols, value));
using namespace std;
int main(int argc, char const * argv[]){
    vector<int> v(4,-1);
    rep(i,4) cin >> v[i];
    VSORT(v);
    rep(i,3){
        if(v[i+1]-v[i]!=1){
            cout<<"No"<<endl;
            return 0;
        }
    }
    cout<<"Yes"<<endl;
    return 0;
}