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