#include<bits/stdc++.h>
using namespace std;
const int N=30;
char s[N];
int main()
{
	cin>>s;
	int n=strlen(s);
	if(s[0]>='0'&&s[0]<='9')
	{
		cout<<"no";
		return 0;
	}
	for(int i=0;i<=n-1;i++)
	{
		if(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z')
		{
			continue;
		}
		if(s[i]>='0'&&s[i]<='9')
		{
			continue;
		}
		if(s[i]=='_')
		{
			continue;
		}
		cout<<"no";
		return 0;
	}
	cout<<"yes";
	return 0;
}