为什么3 4样例无法过

#include<cstring>
using namespace std; 
int main(){
int a[100000],b[10000];
int n,k,c=0;
cin>>n>>k;
for(int i=1;i<=n;i++){
	if(i%k==0){
		a[i]=i;
		c++;
	} 
	else
	b[i]=i;
}
double sum1=0,sum2=0;
for(int i=0;i<=n;i++){
	sum1+=a[i];
	sum2+=b[i];
}
cout<<fixed<<setprecision(1)<<sum1/c<<" "<<sum2/(n-c);
return 0; 
}