#include <iostream>
#include <deque>
using namespace std;

deque<int> DQ;
int a[5000005];
int n, k;
long long total;

void rez()
{
    scanf("%d %d", &n, &k);
    for(int i = 0; i<n; i++)
        scanf("%d", &a[i]);
    for(int i = 0; i<k; i++)
    {
        while(!DQ.empty() && a[DQ.front()] > a[i])
        {
            DQ.pop_front();
        }
        DQ.push_front(i);
    }
    total+=a[DQ.back()];
    for(int i = k; i<n; i++)
    {
        if(DQ.back() == i-k)
            DQ.pop_back();
        while(!DQ.empty() && a[DQ.front()] > a[i])
        {
            DQ.pop_front();
        }
        DQ.push_front(i);
        total+=a[DQ.back()];
    }
    printf("%lld", total);
}

int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    rez();
    return 0;
}