#include <algorithm>
#include <array>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <optional>
#include <queue>
#include <set>
#include <sstream>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

int main() {
    string s;
    cin >> s;
    unordered_map<char, int32_t> hist;
    for (auto c : s) {
        ++hist[c];
    }
    bool ans = true;
    for (auto &&p : hist) {
        if (p.second > 1) {
            ans = false;
            break;
        }
    }
    cout << (ans ? "YES" : "NO") << endl;
    return 0;
}