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