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