#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define coutf(f) cout << fixed << setprecision(f)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()

int main() {
	string s;
	cin >> s;
	sort(all(s));
	rep(i, s.size() - 1) {
		if (s[i] == s[i + 1]) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}