import std.stdio, std.string, std.conv, std.range;
import std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, std.random, core.bitop;

void scan(T...)(ref T args) {
    auto line = readln.split;
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront;
    }
    assert(line.empty);
}

void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}

bool chmin(T, U...)(ref T x, U args) {
    bool isChanged;
    foreach (arg; args) if (x > arg) {
        x = arg;
        isChanged = true;
    }
    return isChanged;
}

bool chmax(T, U...)(ref T x, U args) {
    bool isChanged;
    foreach (arg; args) if (x < arg) {
        x = arg;
        isChanged = true;
    }
    return isChanged;
}



enum inf = 1_001_001_001;
enum infl = 1_001_001_001_001_001_001L;

void main() {
    auto a = readln.split.to!(int[]).sort();
    if (a[0] + 1 == a[1] && a[1] + 1 == a[2] && a[2] + 1 == a[3]) {
        writeln("Yes");
    }
    else {
        writeln("No");
    }
}

struct FenwickTree(T) {
    private {
        int _size;
        T[] _data;
    }

    this(int N) {
        _size = N;
        _data = new T[](_size + 1);
    }

    void add(int i, T x) {
        i++;
        while (i <= _size) {
            _data[i] += x;
            i += i & (-i);
        }
    }

    T sum(int r) {
        T res = 0;
        while (r > 0) {
            res += _data[r];
            r -= r & (-r);
        }
        return res;
    }
}

unittest {
    auto ft = FenwickTree!(int)(10);
    ft.add(0, 3);
    ft.add(2, 4);
    ft.add(5, 1);
    assert(ft.sum(0) == 0);
    assert(ft.sum(1) == 3);
    assert(ft.sum(2) == 3);
    assert(ft.sum(3) == 7);
    assert(ft.sum(5) == 7);
    assert(ft.sum(6) == 8);
}