#include <stdio.h>
#include <deque>

using namespace std;

long long sum;
int a,n,k;
deque < pair<int,int> > dq;

int main()
{
    freopen ("deque.in","r",stdin);
    freopen ("deque.out","w",stdout);

    scanf("%d %d", &n, &k);
    for(int i=1;i<=n;++i)
    {
        scanf("%d", &a);

        while( !dq.empty() && a < dq.back().first )
            dq.pop_back();
        if(!dq.empty() && dq.front().second == i-k)
            dq.pop_front();
        dq.push_back( pair<int,int> (a,i) );
        if(i >= k)
            sum += dq.front().first;
    }
    printf("%lld", sum);
    return 0;
}