#include <fstream>
#define Nmax 5000005
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int a[Nmax], d[Nmax], i, n, k, fata, spate;
long long s;
int main()
{
    fin >> n >> k;
    for(i=1;i<=n;i++)
        fin >> a[i];
    fata=1;
    for(i=1;i<=n;i++)
    {
        while(fata<=spate&&a[i]<=a[d[spate]])
            spate--;

        spate++;
        d[spate]=i;

        if(d[fata]==i-k)
            fata++;

        if(i>=k)
            s+=a[d[fata]];
    }
    fout << s;
    return 0;
}