GKG FIbonacci (works 5000+)

#include <stdio.h>
#include<iostream>
using namespace std;
#define ll unsigned long long
/* Helper function that multiplies 2 matrices F and M of size 2*2, and
puts the multiplication result back to F[][] */
void multiply(ll F[2][2], ll M[2][2]);

/* Helper function that calculates F[][] raise to the power n and puts the
result in F[][]
Note that this function is designed only for fib() and won't work as general
power function */
void power(ll F[2][2], ll n);

ll fib(ll n)
{
ll F[2][2] = {{1,1},{1,0}};
if (n == 0)
	return 0;
power(F, n-1);

return F[0][0];
}

void multiply(ll int F[2][2], ll int M[2][2])
{
ll x = F[0][0]*M[0][0] + F[0][1]*M[1][0];
ll int y = F[0][0]*M[0][1] + F[0][1]*M[1][1];
ll int z = F[1][0]*M[0][0] + F[1][1]*M[1][0];
ll int w = F[1][0]*M[0][1] + F[1][1]*M[1][1];

F[0][0] = x;
F[0][1] = y;
F[1][0] = z;
F[1][1] = w;
}

void power(ll F[2][2],ll int n)
{
ll int i;
ll int M[2][2] = {{1,1},{1,0}};

// n - 1 times multiply the matrix to {{1,0},{0,1}}
for (i = 2; i <= n; i++)
	multiply(F, M);
}

/* Driver program to test above function */
int main()
{
ll int n=5010;
cout<<fib(n);
///printf("%d", fib(n));
getchar();
return 0;
}
//https://www.geeksforgeeks.org/program-for-nth-fibonacci-number/