#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    string s;
    cin >> s;
    
    int p[256] = {};
    for (const auto& c : s) {
        p[c]++;
    }

    int b = 1;
    for (int i = 0; i < 256; i++) {
        if (p[i] > 1) b = 0;
    }

    cout << (b ? "YES" : "NO") << endl;

    return 0;
}