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