why???????????? 75!!!!!!

#include <bits/stdc++.h>
using namespace std;
int main() {
	long long n, k, p, a = 1, b = 0, i = 2, x;
	cin >> n >> k >> p;
	while (i <= n) {
		x = a;
		a = a + b;
		if (i >= 3 && a % k == 1)
			a--;
		if (a > k * p)
			a = a % (k * p);
		b = x;
		i++;
	}
	cout<<a%p;
	return 0;
}

help!