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