#include <bits/stdc++.h> using namespace std; char x[21]; int main(){ cin >> x; if(x[0] >= 48 && x[0] <= 57){ cout << "no"; return 0; } for(int i = 1;i < strlen(x);i++){ int p = x[i]; if((p<'a' && p>'z') && (p<'A' && p>'Z') && p!='_'){ cout << "no"; return 0; } } cout << "yes"; return 0; }