#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
using namespace std;
string s;
int main()
{
	int l,i,k=0;
	cin>>s;
	l=s.size();
	if(s[0]>='0'&&s[0]<='9')
	{
		cout<<"no";
		return 0;
	}
	for(i=1;i<=l-1;i++)
	{
		if(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'||s[i]>='0'&&s[i]<='9'||s[i]=='_')
		{
			k++;
		}
	}
	if(k==l-1)cout<<"yes";
	else cout<<"no";
	return 0;
}