题……解？（魔怔

#include <bits/stdc++.h>
#define c char
const int z = -0xffffffff - 1;
const std::string on = "1";
class _int {
public:
    std::string n;
    
    std::string O(std::string a, std::string b) {
        int carry = 0, i = a.size() - 1, j = b.size() - 1;
        std::string result;
        
        while (i >= 0 || j >= 0 || carry) {
            int digit1 = (i >= 0) ? (a[i] - '0') : 0;
            int digit2 = (j >= 0) ? (b[j] - '0') : 0;
            int sum = digit1 + digit2 + carry;
            carry = sum / 10;
            sum %= 10;
            result += (sum + '0');
            
            if (i >= 0) i--;
            if (j >= 0) j--;
        }
        
        reverse(result.begin(), result.end());
        return result;
    }
    
    std::string _P(std::string a, std::string b) {
        std::string product;
        for (int i = 0; i < a.size(); i++) {
            for (int j = 0; j < b.size(); j++) {
                int digit1 = a[i] - '0';
                int digit2 = b[j] - '0';
                int prod = digit1 * digit2;
                product += (prod + '0');
            }
        }
        return product;
    }
};

int main() {
    _int a, b;
    std::cin >> a.n >> b.n;
    
    std::string sum_result = a._P(a.O(a.n, b.n) ,on);
    std::cout << sum_result;
    return 0;
}