#include <bits/stdc++.h>
using namespace std;
char x[21];
int main(){
	cin >> x;
	if(x[0] >= 48 && x[0] <= 57){
		cout << "no";
		return 0;
	}
	for(int i = 1;i < strlen(x);i++){
		int p = x[i];
		if((p<'a' && p>'z') && (p<'A' && p>'Z') && p!='_'){
			cout << "no";
			return 0;
		}
	}
	cout << "yes";
	return 0;
}