#include <fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int n,i,k,a[5000010],deque[5000010];
int l,r;
long long suma;

int main()
{
    fin>>n>>k;
    for(i=1;i<=n;++i) fin>>a[i];

    l=1; r=0;

    for(i=1;i<=n;++i)
    {
        while(l<=r && a[i]<=a[deque[r]]) r--;
        deque[++r]=i;

        if(deque[l]==i-k) l++;

        if(i>=k) suma+=a[deque[l]];
    }

    fout<<suma;
        return 0;
}