#include <cstdio>
#include <deque>
#define Nmax 5000010
using namespace std;
deque < int > deq;
long long suma;
int vec[Nmax];
int n,k;
void read()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d",&n,&k);
    for(int i = 1 ; i <= n ; i++)
    {
        scanf("%d ",&vec[i]);
        while(!deq.empty() && vec[deq.back()] >= vec[i])
            deq.pop_back();
        deq.push_back(i);
        if(i >= k)
        {

            if( deq.front() <= i - k )
            deq.pop_front();

            suma += vec[deq.front()];
        }
    }
}

int main()
{
    read();
    printf("%d",suma);
    return 0;
}