#include<bits/stdc++.h>
using namespace std;
int main(){
	string s;
	cin>>s;
	for(int i=0;i<s.size();i++){
		if(i==0){
			if(!((s[i]>='a'&&s[i]<='z')||(s[i]>='A'&&s[i]<='Z')||(s[i]=='_'))){
				cout<<"no";
				return 0;
			}
		}else{
			if(!(
				(s[i]>='a'&&s[i]<='z')
				||
				(s[i]>='A'&&s[i]<='Z')
				||
				(s[i]>='0'&&s[i]<='9')
				||
				(s[i]=='_')
				)
			){
				cout<<"no";
				return 0;
			}
		}
		
	}
	cout<<"yes";
	return 0;
}