#include<iostream> using namespace std; bool islegitimate(string s){ if(s[0]>='0'&&s[0]<='9') return 0; int lens=s.size(); for(int i=0;i<lens;i++){ if(s[i]>='A'&&s[i]<='Z'||s[i]>='a'&&s[i]<='z'||s[i]>='0'&&s[i]<='9'||s[i]=='_') continue; return 0; } return 1; } int main(){ string s; cin>>s; if(islegitimate(s)) cout<<"yes"; else cout<<"no"; return 0; }