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

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

reader.on('close', () => {
    var num = parseInt(lines);
    num.sort();
    var A = num[0];
    var B = num[1];
    var C = num[2];
    var D = num[3];
    
    if(D - C == 1 && C - B == 1 && B - A == 1){
        console.log('Yes');
    } else {
        console.log('No');
    }
});