#include <fstream>

using namespace std;

int n,k,i,cap = 1,coada = 0;

long long s = 0;

int main()
{
    int a[5000000],deque[5000000];
    ifstream f("deque.in");
    ofstream g("deque.out");
    f >> n >> k;
    for (i=0; i<n; i++)
        f >> a[i];
    for (i=0; i<n; i++)
    {
        while ((cap<=coada)&&(a[i]<=a[deque[coada]])) coada--;

        deque[++coada]=i;

        if (i>=k-1) s+=a[deque[cap]];

        if (deque[cap]==i-k+1) cap++;
    }
    g << s;
    return 0;
}