#include <stdio.h>
using namespace std;
FILE *f=fopen("deque.in","r");
FILE *g=fopen("deque.out","w");

int v[5000330],deque[5000300];
int i,n,k,b,p;
long long s;
int main()
{

fscanf(f,"%d%d",&n,&k);

for(i=1;i<=n;i++)
fscanf(f,"%d",&v[i]);
p=1;
b=0;

for(i=1;i<=n;i++)
{
 while(p<=b && v[i]<=v[deque[b]])b--;
 b++;
 deque[b]=i;
 if (deque[p]==i-k)p++;
 if(i>=k)s=s+v[deque[p]];
}


 fprintf(g,"%lld",s);
    fclose(g);
    return 0;
}