Karatsuba Trick using C++

#include <bits/stdc++.h>

using namespace std;

const int MOD = (int) 1e9 + 7;

long long Karatsuba(long long x, long long y) {
    // ((10 ^ 6) * a + b) * ((10 ^ 6) * c + d)
    // = ((10 ^ 12) * a * c) + ((10 ^ 6) * ((a * d) + (b * c))) + (b * d)
    // where a, b, c, are (10 ^ 6)-digit numbers
    long long a = x / 1000000;
    long long b = x % 1000000;
    long long c = y / 1000000;
    long long d = y % 1000000;
    // first expression = ((10 ^ 12) * a * c)
    long long first_expression = ((1000000000000LL * a % MOD) * c) % MOD;
    // second expression = ((10 ^ 6) * ((a * d) + (b * c)))
    long long second_expression = (1000000 * (((a * d) + (b * c)) % MOD)) % MOD;
    // third expression = (b * d)
    long long third_expression = b * d;
    return ((first_expression + second_expression + third_expression) % MOD);
}

int main() {
    // constraints: 1 <= x, y <= (10 ^ 12)
    // note: answer must be computed to modulo ((10 ^ 9) + 7)
    long long x, y;
    cin >> x >> y;
    cout << Karatsuba(x, y) << '\n';
    return 0;
}