#include <iostream>
#include <deque>
#define MAX 5000000
using namespace std;

int n,k,a[MAX];
long long int s;
deque <int> Q;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);

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

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