include<bits/stdc++.h>

using namespace std; int main() {

char a[300];
cin.getline(a,300);
int len = strlen(a);
if(a[0]>='0'&&a[0]<='9')
{
	cout<<"no";
	return 0;
}
for(int i=0;i<len;i++)
{
	if(!((a[i]>='0'&&a[i]<='9')||(a[i]>=65&&a[i]<=90)||(a[i]>=97&&a[i]<=122)||a[i]=='_'))
	{
		cout<<"no";
		return 0;
	}
}
cout<<"yes";
return 0;

}