#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; }