#include <deque>
#include <cstdio>

#define poz first
#define x second
using namespace std;

deque < pair<int, int> > dq;

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

    scanf("%d%d",&n,&k);
    scanf("%d",&nr);
    dq.push_back(make_pair(1,nr));
    for(int i =2;i <= k;i++)
    {
        scanf("%d",&nr);
        while(!dq.empty() && dq.back().x > nr)
        {
            dq.pop_back();
        }
        dq.push_back(make_pair(i,nr));
    }

    long long sol = dq.front().x;
    for(int i=k+1;i<=n;i++)
    {
        if(i - k + 1 > dq.front().poz)
             dq.pop_front();

        scanf("%d",&nr);
        while(!dq.empty() && dq.back().x > nr)
        {
            dq.pop_back();
        }
        dq.push_back(make_pair(i,nr));
        sol += dq.front().x;
    }

    printf("%lld",sol);
}