#include <iostream>
#include <fstream>
#define nmax 5000010

using namespace std;

int a[nmax];
int d[nmax];
int f,b;
long long sum;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    int n,k;
    scanf("%d %d",&n,&k);

    for(int i=1;i<=n;i++)
        scanf("%d ",&a[i]);

    f=1,b=0;
    for(int i=1;i<=n;i++)
    {
        while( f <= b && a[i] <= a[d[b]]) b--;

        d[++b] = i;

        if(d[f] == i-k) f++;

        if(i>=k)
            sum += a[d[f]];
    }
    printf("%lld\n",sum);
    return 0;
}