#include <deque>
#include <cstdio>
using namespace std;

deque < pair <int,int> > c;
long long rez;
int n,k;

int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int i,x;
    scanf("%d%d%d",&n,&k,&x);
    c.push_front( make_pair(x,1));
    for(i=2;i<=k-1;i++)
    {
        scanf("%d",&x);
        while(!c.empty() && c.back().first>=x) c.pop_back();
        c.push_back(make_pair(x,i));
    }

    for(i=k;i<=n;i++)
    {
        scanf("%d",&x);
        if(c.front().second==i-k) c.pop_front();
        while(!c.empty() && c.back().first>=x) c.pop_back();
        c.push_back(make_pair(x,i));
         rez+=c.front().first;
    }
    printf("%lld\n",rez);
    fclose(stdin);
    fclose(stdout);
    return 0;
}