为啥错了？

#include<bits/stdc++.h>
using namespace std;
unsigned long long n,k,p;
int main(){
	cin>>n>>k>>p;
    vector<unsigned long long> a(n+5);
	a[1]=1,a[2]=1;
	for(unsigned long long i=3;i<=n;i++){
		a[i]=a[i-1]+a[i-2];
		if(a[i]%k==1) a[i]--; 
	}
	cout<<a[n]%p;
	return 0;
}