big fibonacci modulo m c++

#include <iostream>
#include <unordered_map>

using namespace std;

unordered_map<long long, long long> Fib;

long long fib(long long n)
{
    if (n < 2) return 1;
    if (Fib.find(n) != Fib.end()) return Fib[n];
    Fib[n] = (fib((n + 1) / 2) * fib(n / 2) + fib((n - 1) / 2) * fib((n - 2) / 2)) % 1000000007;
    return Fib[n];
}

int main()
{
    long long N;
    cin >> N;
    cout << fib(N);
}