#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(n);++i)
#define all(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	string S;
	cin >> S;
	string T = S;
	sort(all(S));
	auto result = unique(all(S));
	S.erase(result, S.end());
	if (S.size() == T.size()) cout << "YES" << endl;
	else cout << "NO" << endl;
	return 0;
}