C++ :

#include <iostream>
using namespace std;
string octalToBinary(char octalDigit) {
    switch (octalDigit) {
        case '0': return "000";
        case '1': return "001";
        case '2': return "010";
        case '3': return "011";
        case '4': return "100";
        case '5': return "101";
        case '6': return "110";
        case '7': return "111";
        default: return "";
    }
}
void convertOctalToBinary(string octal) {
    string binary = "";
    for (char digit : octal) {
        binary += octalToBinary(digit);
    }
    // 去除多余的前导零
    int start = 0;
    while (start < binary.length() && binary[start] == '0') {
        start++;
    }
    if (start == binary.length()) {
        cout << "0" << endl;  // 特殊情况，输入为 0 时
    } else {
        cout << binary.substr(start) << endl;
    }
}
int main() {
    string octal;
    cin >> octal;
    convertOctalToBinary(octal);
    return 0;
}