#include <bits/stdc++.h>

using namespace std;

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

int a[5000001], i,x,k,n;
long long s;
deque<pair<int,int>> d;

int main()
{
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>a[i];
    for (i=1;i<=k;i++)
    {while (!d.empty()&&d.front().first>a[i])
        d.pop_front();
    d.push_front(make_pair(a[i], i));
    }
    auto t=d.back();
    s+=t.first;
    for (i=k+1;i<=n;i++)
    {
        auto t =d.back();
        if (t.second<=i-k)
            d.pop_back();
        while(!d.empty()&&d.front().first>a[i])
            d.pop_front();
        d.push_front(make_pair(a[i],i));
        t=d.back();
        s+=t.first;
    }
    fout<<s;
    return 0;
}