#include <cstdio>
#include <cstdlib>
#include <cmath>
using namespace std;

#define nmax 5000010

int v[nmax], deque[nmax], N, K, front, back;
long long sum;


int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    int i;
    scanf("%i %i", &N, &K);
    for(i = 1; i <= N; i++) scanf("%i", &v[i]);
    front = 1; back = 0;
    for(i = 1; i <= N; i++)
    {
          while(front <= back && v[i] <= v[ deque[back] ]) back --;
          deque[++ back] = i;
          if(deque[front] == i - K) front ++;
          if(i >= K) sum += 1LL * v[ deque[front] ];
    }
    printf("%lld\n", sum);
    return 0;
}