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