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