//parsare - daca e nevoie
#include <stdio.h>
#define NMAX 5000023
FILE *fin, *fout;
int n, k, dr = 0, st = 1, temp;
long long int sum;
bool f;
struct deq
{
       int val;
       int poz;
} d[NMAX];
int main()
{
    fin = fopen("deque.in", "r");
    fout = fopen("deque.out", "w");
    fscanf(fin, "%d%d", &n, &k);
    for(int i = 1; i< k; i++)
    {
            fscanf(fin, "%d", &temp);
            if(!f)
            {
                  dr++;
                  d[dr].val = temp;
                  d[dr].poz = i;
                  f = 1;
                  continue;
            }
            while(dr>=st && temp<=d[dr].val)
            {
                         dr--;
            }
            dr++;
            d[dr].val = temp;
            d[dr].poz = i;
    }
    for(int i = k; i<=n; i++)
    {
            fscanf(fin, "%d", &temp);
            if(d[st].poz <= i - k) st++;
            while(dr>=st && temp<=d[dr].val)
            {
                         dr--;
            }
            dr++;
            d[dr].val = temp;
            d[dr].poz = i;
            sum+=(int)d[st].val;
    }
    fprintf(fout, "%lld\n", sum);
    fclose(fin);
    fclose(fout);
    return 0;
}