#include <cstdio>
#include <deque>
using namespace std;

FILE* in=fopen("deque.in", "r");
FILE* out=fopen("deque.out", "w");
deque<pair<int, int> > d; 

int main()
{
	int n, k;
	
	fscanf(in, "%d%d", &n, &k);
	
	int x;
	fscanf(in, "%d", &x);
	d.push_back(make_pair(x, 1));
	
	long long sum=0;
	for(int i=2; i<=n; ++i)
	{
		fscanf(in, "%d", &x);
		while(!d.empty()&&d.back().first>=x) d.pop_back();
		d.push_back(make_pair(x, i));
		while(!d.empty()&&d.front().second+k-1<i) d.pop_front();
		if(i>=k) sum+=d.front().first;
	}
	fprintf(out, "%lld", sum);
}