#include <iostream>

using namespace std;

bool sort(int *a, int *b, int *c, int *d) {
    bool result = false;
    int *buf;
    if (a>b) {
        buf = a;
        a = b;
        b = buf;
        result = true;
    }
    if (b>c) {
        buf = b;
        b = c;
        c = buf;
        result = true;
    }
    if (c>d) {
        buf = c;
        c = d;
        d = buf;
        result = true;
    }
    return result;
}
int main () {
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    for(;sort(&a,&b,&c,&d);){}
    if(d-1==c && c-1==b && b-1==a) {
        cout<<"Yes"<<endl;
    } else {
        cout<<"No"<<endl;
    }
    return 0;
}