#include <cstdio>

int n,k,p,u;
int a[5000001],deq[5000001];
long long sum;

int main()
{
    int i;
    FILE *f=fopen("deque.in","r");
    FILE *g=fopen("deque.out","w");
    fscanf(f,"%d %d",&n,&k);
    for(i=1;i<=n;i++)fscanf(f,"%d",&a[i]);
    p=1;u=0;sum=0;
    for(i=1;i<=n;i++)
    {
        while(p<=u&&a[i]<=a[deq[u]]) u--;
        deq[++u]=i;
        if(deq[p]==i-k)p++;
        if(i>=k)sum+=a[deq[p]];
    }
    fprintf(g,"%lld",sum);
    fclose(f);
    fclose(g);
    return 0;
}