#include<bits/stdc++.h> using namespace std; int main(){ string a; cin>>a; int cnt=0; bool x=1; for(int i=0;i<a.size();i++) if(!(a[i]>='0'&&a[i]<='9'||a[i]>='a'&&a[i]<='z'||a[i]>='A'&&a[i]<='Z'||a[i]==95)) x=0; if(a[0]>='0'&&a[0]<='9') x=0; if(x==1) cout<<"yes"; else cout<<"no"; return 0; }