Прямой и обратный хеш

#include <iostream>
#include <string>


int mod = 1000000007;

int forward (std::string s, int k) {
    int h = 0;
    int m = 1;
    for (char c : s) {
        int x = (int) (c - 'a' + 1);
        h = (h + m * x) % mod;
        m = (m * k) % mod;
    }
    return h;
}

int back (std::string s, int k) {
    int h = 0;
    for (char c : s) {
        int x = (int) (c - 'a' + 1);
        h = (h * k + x) % mod;
    }
    return h;
}

int main() {
    std::string s;
    int k = 0;
    int f = 0;
    int b = 0;
    std::cin >> s >> k;
    f = forward(s, k);
    b = back(s, k);
    std::cout << f << std::endl << b;
}