#include <cstdio>
#include <vector>
#include <deque>
#define x first
#define y second
using namespace std;
int n,k;
typedef pair<int,int> punct;
deque<punct> d; punct aux;
long long Sum=0;
int main()
{freopen("deque.in", "rt", stdin);
 freopen("deque.out", "wt", stdout);
 scanf("%d%d",&n,&k);
 for (register int i=0;i<n;++i)
	{scanf("%d",&aux.x);aux.y=i;
	 while (!d.empty() && aux.x<d.back().x) d.pop_back();		
	 d.push_back(aux);
	 if (d.front().y == i-k) d.pop_front();
	 if (i >= k-1) Sum += d.front().x; 	
	}
 printf("%lld\n",Sum);
 return 0;
}