#include <cstdio>
#define MX 5000001
//using namespace std;

FILE *fin, *fout;
int n,k;
int a[MX], s[MX];
long long suma;

void citire()
{
    int i;
    fscanf(fin, "%d%d", &n, &k);
    for(i=1; i<=n; i++) fscanf(fin, "%d", &a[i]);
}

int main()
{
    fin = fopen("deque.in", "r");
    fout = fopen("deque.out", "w");

    int i,l=1,d=0;
    citire();

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

        s[++d] = i;

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

        if(i >= k) suma += a[s[l]];
    }
    fprintf(fout, "%lld", suma);

    fclose(fin); fclose(fout);
    return 0;
}