#include<bits/stdc++.h> using namespace std; int main() { string a; getline(cin,a); int s=a.size(); int l=1; for(int i=0;i<s;i++){ if((a[i]>='a'&&a[i]<='z')||(a[i]>='A'&&a[i]<='Z')||(a[i]>='0'&&a[i]<='9')||a[i]=='_'){ l=1; }else{ l=0; cout<<"no"; return 0; } }if(a[0]>='0'&&a[0]<='9')l=0; else l=1; if(l==1)cout<<"yes"; else cout<<"no"; return 0; }