process.stdin.resume();
process.stdin.setEncoding('utf8');

var lines = []
var reader = require('readline').createInterface({
    input: process.stdin,
    output: process.stdout
});

reader.on('line', (line) => {
    lines.push(line);
});

reader.on('close', () => {
    const arr = lines[0].split(' ').map(hoge=>parseInt(hoge, 10));
    var newArr = function(a, b){
        return a - b;
    }
    arr.sort(newArr);
    if(arr[3] - arr[2] == 1 && arr[2] - arr[1] == 1 && arr[1] - arr[0] == 1){
        console.log('Yes');
    } else {
        console.log('No');
    }
});