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