#include<bits/stdc++.h> using namespace std; string s; int main() { cin>>s; int n=s.size(); if(s[0]>='0'&&s[0]<='9') { cout<<"no"; return 0; } for(int i=1; i<n; i++) { if(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'||s[i]>='0'&&s[i]<='9'||s[i]=='_') { } else { cout<<"no"; return 0; } } cout<<"yes"; return 0; }