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