import std.stdio;
import std.array;
import std.string;
import std.conv;

void main() {
    string s = chomp(readln());

    int[char] counter;
    foreach (c; s) {
        counter[c]++;

        if (counter[c] > 1) {
            writeln("NO");
            return;
        }
    }
    writeln("YES");
}