#include <stdio.h>

int n,k,lol[5000005], poz[5000005];
long long S;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int p,u;
    scanf("%d %d",&n,&k);
    for (int i=1;i<=n;i++)
          scanf("%d",&lol[i]);

    p=1;u=0;
    for (int i=1;i<=n;i++)
    {
        while (lol[i]<=lol[poz[u]] && u>=p)
               u--;
        lol[++u]=i;
        if (poz[p]==i-k)
               p++;
        if (i>=k)
          S+=lol[poz[p]];
    }
    printf("%lld\n",S);
    return 0;
}