std::string sum(const std::string& a, const std::string& b);
​
int main() {
    std::string a;
    std::cin >> a;
    std::string b;
    std::cin >> b;
​
    std::cout << sum(a, b);
​
    return 0;
}
​
std::string sum(const std::string& a, const std::string& b) {
    std::string sum;
    int i = a.size() - 1;
    int j = b.size() - 1;
    int one = 0;
    while ((i >= 0) || (j >= 0)) {
        char ai = (i >= 0) ? a[i] : '0';
        char bj = (j >= 0) ? b[j] : '0';
        int s = static_cast<int>(ai - 48) +
                static_cast<int>(bj - 48) + one;
        if (s >= 10) {
            sum = static_cast<char>(s - 10 + 48) + sum;
            one = 1;
        } else {
            sum = static_cast<char>(s + 48) + sum;
            one = 0;
        }
        --i;
        --j;
    }
    if (one == 1)
        sum = '1' + sum;
    return sum;
}
​