#include<cstdio>
using namespace std;
FILE *in=fopen("deque.in","r");
FILE *out=fopen("deque.out","w");
long long sum;
int n,k,x,deq[5000005],a[5000005],bottom,top;
int main(){
    fscanf(in,"%d%d",&n,&k);
    for(int i=1;i<=n;i++)
    {
        fscanf(in,"%d",&a[i]);
        while(bottom<=top && a[i]<=a[deq[top]]) --top;
        deq[++top]=i;
        if(deq[bottom]==i-k) ++bottom;
        if(i>=k) sum+=a[deq[bottom]];
    }
    fprintf(out,"%lld",sum);
}