#include <bits/stdc++.h>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
long long N, K, Sum, x;
struct str
{
    long long nr, in;
};
deque <str> dq;
int main()
{
    in >> N >> K;
    for(int i = 1;i <= N;i++)
    {
        in >> x;
        while(!dq.empty() && dq.back().nr >= x)
            dq.pop_back();
        dq.push_back({x, i});
        if(i >= K)
        {
            Sum += dq.front().nr;
            if(dq.front().in == i - K + 1)
                dq.pop_front();
        }
    }
    out << Sum;
    return 0;
}