#include <bits/stdc++.h>
#define LL long long

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

LL sum;
int n, k, x, index;
deque<pair<int, int> > d; /// pair( element, index )

int main()
{
    fin >> n >> k >> x;
    d.push_front(make_pair(x, 1));
    for(index=2; index<=k; index++)
    {
        fin >> x;
        while(d.back().first >= x)
            d.pop_back();
        d.push_back(make_pair(x,index));
    }
    sum = d.front().first;
    for(; index<=n; index++)
    {
        fin >> x;
        while(d.back().first >= x)
            d.pop_back();
        d.push_back(make_pair(x,index));
        while(index - d.front().second == k)
            d.pop_front();
        sum+=d.front().first;
    }
    fout<<sum;
    return 0;
}