#include <bits/stdc++.h>
#define int long long
using namespace std;
const int mod=1e9+7;
typedef long long ll;
int n,k,a[1000005],ans,m,b[1000005],x;
signed main()
{
cin>>n>>k;
for(int i=0;i<n;i++)
{
cin>>a[i];
}
cin>>m;
int st=0;
while(1)
{
ans=ans+a[x];
b[++st]=ans;
x=(x+k+1)%n;
if(x==0)break;
}
cout<<(((ans%mod)*(m/st)%mod)%mod+(b[m%st])%mod+mod)%mod;
}
题目https://www.xinyoudui.com/ac/contest/747004E6E00060F031A1B26/problem/8510
