#include<iostream>
#include<cstring>
typedef long long LL;
const int Max = 1e6 + 5;
using namespace std; 

LL b[Max];//b为前缀和序列 
int main()
{
	LL x,n,k,i,j,M = 0,ans;//m为可以传送的最大距离 
	cin >> n >> k;
	for(i = 0;i < n - 1; ++i)
	{
		cin >> x;
		if(i == 0) b[0] = x;
		else b[i] = x + b[i - 1];
		int f = i - k < 0 ? 0 : i - k;
		M = max(M,b[i] - b[f]); 
	}
	ans = b[n - 2] - M;
	cout << ans;
	return 0;
}```