#include <bits/stdc++.h>
using namespace std;
int main(){
    string a;
    int len;
    int i;
    getline(cin,a);
    len=a.length();
    if(a[0]>='0'&&a[0]<='9'){
        cout<<"no"<<endl;
        return 0;
    }
    for(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"<<endl;
        return 0;
    }
    }
    cout<<"yes"<<endl;
        return 0;
}