#include <bits/stdc++.h>
using namespace std;

int main() {
	string s;
	cin >> s;
	if (s.empty()) {
		cout << "no";
		return 0;
	}
	if (!(isalpha(s[0]) || s[0] == '_')) {
		cout << "no";
		return 0;
	}
	for (int i = 1; i < (int)s.size(); i++) {
		char c = s[i];
		if (!(isalnum(c) || c == '_')) {
			cout << "no";
			return 0;
		}
	}
	
	cout << "yes";
	return 0;
}