#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;
}

#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; return 0; }

#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; return 0; }