import std.stdio, std.string, std.conv, std.range, std.array, std.algorithm;
import std.uni, std.math, std.container, std.typecons, std.typetuple;
import core.bitop, std.datetime;

immutable int mod = 10^^9 + 7;

void main()
{
    auto s = readln.chomp.to!(dchar[]);
    auto rbt = redBlackTree(s);

    if (s.length == rbt.length) {
        writeln("yes");
    }
    else {
        writeln("no");
    }
}

void readVars(T...)(auto ref T args)
{
    auto line = readln.split;
    foreach(ref arg ; args){
        arg = line.front.to!(typeof(arg));
        line.popFront;
    }
    if(!line.empty){
        writeln(line);
        throw new Exception("args num < input num");
    }
}