#include<stdio.h>
#define N 5000001
int n,k,i,q[N],a[N],p,u;
long long s;
int main() 
{
    freopen("deque.in","r",stdin),freopen("deque.out","w",stdout),scanf("%d%d",&n,&k);
    for(p=i=1;i<k;i++)
    {
    	scanf("%d",a+i);
    	for(;p<=u&&a[i]<=a[q[u]];u--);
        q[++u]=i;
	}
    for(p=i=1;i<=n;i++)
    {
        scanf("%d",a+i);
        for(;p<=u&&a[i]<=a[q[u]];u--);
        q[++u]=i;
        if(q[p]==i-k)
            p++;
        if(i>=k)
            s+=a[q[p]];
    }
    printf("%lld",s);
}