#include <bits/stdc++.h>
using namespace std;

int main(){
    std::string a;
    int i = 0;
    char b[1005];
    cin>>a;
    std::string str = a;
    for (char c : str) {
        i++;
        b[i] = c;
    }
    for(int k = 0;k <= 9;k++)if(b[1] == k + '0'){
        cout<<"no"; 
        return 0;
    }
    for(int j = 2;j <= i;j++){
        for(int k = 0;k <= 9;k++){
            for(char m = 65;m <= 90;m++){
                for(char l = 'a';l <= 'z';l++){
                    if((b[i] != '_' && b[i] != k + '0' && b[i] != m && b[i] != l) || b[i] == ' '){
                        cout<<"no";
                        return 0;
                    }
                        else{
                            cout<<"yes";
                            return 0;
                        }
                }
            }
        }
    }
}

AC必关，50分求调！

希望使用枚举法 QAQ