#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 < k ; i++)
    {
        scanf("%d ",&vec[i]);
        while(!deq.empty() && vec[deq.back()] >= vec[i])
            deq.pop_back();
        deq.push_back(i);
    }
    for(int i = k ; i <= n ; i++)
        {
            scanf("%d ",&vec[i]);
            if(!deq.empty() && deq.front() <= i - k )
                deq.pop_front();
            while(!deq.empty() && vec[deq.back()] >= vec[i])
                deq.pop_back();
            deq.push_back(i);
            suma += vec[deq.front()];
        }
}

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