#include <iostream>
#include <fstream>
#include <deque>

using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");

#define ll long long
#define pb push_back
const int NMax = 5e6 + 5;

int N,K;
int v[NMax];
deque<int> deq;

int main() {
    in>>N>>K;

    ll sum = 0;
    for (int i=1;i <= K;++i) {
        in>>v[i];

        while (deq.size() && v[deq.back()] >= v[i]) {
            deq.pop_back();
        }
        deq.push_back(i);
    }

    sum += v[deq.front()];

    for (int i=K+1;i <= N;++i) {
        in>>v[i];

        if (deq.front() == i-K) {
            deq.pop_front();
        }

        while (deq.size() && v[deq.back()] >= v[i]) {
            deq.pop_back();
        }
        deq.push_back(i);

        sum += v[deq.front()];
    }

    out<<sum<<'\n';

    in.close();out.close();
    return 0;
}