#include <cstdio>
#include <deque>
#define N 5000005
using namespace std;

int n, k, a[N];
long long int s;
deque <int> d;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

    scanf("%d %d\n",&n, &k);
    for (int i=0;i<n;i++)
        scanf("%d\n",&a[i]);

    for (int i=0;i<k-1;i++)
    {
        while(!d.empty() && a[d.back()]>a[i])
            d.pop_back();
        d.push_back(i);
    }

    for (int i=k-1;i<n;i++)
    {
        while(!d.empty() && a[d.back()]>a[i])
            d.pop_back();
        d.push_back(i);
        if(d.front()==i-k)
            d.pop_front();
        s=s+a[d.front()];
    }
    printf("%lld",s);
    return 0;
}