#include<iostream> using namespace std; string s; int main(){ cin>>s; int s1=s.size(); if(s[0]>='0'&&s[0]<='9'){ cout<<"no"; return 0; } int Imsb=0; for(int i=0;i<s1;i++){ if(s[i]>='0'&&s[i]<='9'||s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'||s[i]=='_'){ Imsb++; }else{ cout<<"no"; return 0; } } cout<<"yes"; return 0; }