#include <cstdio>
#include <deque>
using namespace std;
#define mp make_pair

deque<pair<int,int> >d;
long long s=0;
int n,k;

int main()
{
    int x;
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
        scanf("%d %d",&n,&k);
        for(int i=1;i<=k;i++)
        {
            scanf("%d",&x);
            while(d.size()>0 && d.back().second>=x)d.pop_back();
            d.push_back(mp(i,x));
        }
        s=d.front().second;
        for(int i=k+1;i<=n;i++)
        {
            scanf("%d",&x);
            while(d.size()>0 && d.back().second>=x)d.pop_back();
            while(d.size()>0 && d.front().first<=i-k)d.pop_front();
            d.push_back(mp(i,x));
            s+=d.front().second;
        }
        printf("%lld\n",s);
    return 0;
}