var num = [1,2,3,4];
var sort = num.sort(function(a,b){
    return b - a;
});
var answer = function(a,b,c,d){
var a = sort[0];
var b = sort[1];
var c = sort[2];
var d = sort[3];
    if(a - b === 1 && b - c === 1 && c - d === 1){
    console.log('YES');
    }else{
    console.log('NO');
    }
}