# include<stdio.h> # include<cstring> # include<iostream> # include<cstdio> using namespace std; int main(){ string a; cin>>a; int len = a.size(); if(a[0]>='0'&&a[0]<='9') { cout<<"no"; return 0; } for(int i=0;i<len;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; }