#include <iostream>
#include <fstream>
#include <queue>
#include <vector>

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

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

int N,K;

struct elem {
    int val,ord;
    elem (int _val = 0,int _ord = 0) {
        val = _val;
        ord = _ord;
    }
};
deque<elem> deq;

int main() {
    in>>N>>K;
    for (int i=1;i <= K;++i) {
        int val;
        in>>val;

        while (deq.size() && deq.back().val >= val) {
            deq.pop_back();
        }

        deq.push_back(elem(val,i));
    }

    ll ans = deq.front().val;

    for (int i=K+1;i <= N;++i) {
        int val;
        in>>val;

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

        while (deq.size() && deq.back().val >= val) {
            deq.pop_back();
        }

        deq.push_back(elem(val,i));

        ans += deq.front().val;
    }

    out<<ans<<'\n';

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