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

void main() {
    auto S = readln.chomp;
    auto N = S.length.to!int;

    auto hoge = new int[](26);

    bool solve(int l, int r) {
        hoge[] = -1;
        foreach (i; l..r+1) {
            int parity = (i - l) & 1;
            int c = S[i] - 'a';
            if (S[i] == ' ') {
                if (parity) return false;
                else continue;
            }
            if (hoge[c] != -1 && hoge[c] != parity) {
                return false;
            }
            hoge[c] = parity;
        }

        foreach (i; 0..l) {
            int c = S[i] - 'a';
            if (hoge[c] == 0) return false;
        }

        foreach (i; r+1..N) {
            int c = S[i] - 'a';
            if (hoge[c] == 0) return false;
        }

        return true;
    }

    foreach (l; 0..N) foreach (r; l..N) if (solve(l, r)) {writeln("Yes"); return;}
    writeln("NO");
}