//#include <iostream>
#include <queue>
#include <stack>
#include <map>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <set>
#include <algorithm>
#include <bitset>
#include <time.h>
#include <tuple>
#include <fstream>
#include <iomanip>
#include <utility>

#pragma warning "da 100% din tine. :)"
#define nl '\n'
#define cnl cout << '\n';
#define sp ' '
#define pb(x) push_back(x)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define ll long long
#define ull unsigned ll
#ifdef INFOARENA
#define ProblemName "deque"
#endif
#define MCONCAT(A, B) A B
#ifdef ProblemName
#define InFile MCONCAT(ProblemName, ".in")
#define OuFile MCONCAT(ProblemName, ".out")
#else
#define InFile "a.in"
#define OuFile "a.out"
#endif

using namespace std;
ifstream cin(InFile);
ofstream cout(OuFile);

template<class v, class type>
void print(v Vector, type nr) {
    for_each(all(Vector), [](type x) {
        cout << x << ' ';
    });
}

void nimic() {
    return;
}

deque<int> dq;
deque<int> poz;
ll sum = 0;
int el;
int A[5000001];

int main() {
    ios_base::sync_with_stdio(false);
    clock_t tStart = clock();
    int k, n;
    cin >> n >> k;
    for (int i = 1; i <= k; ++i) {
        cin >> A[i];
        while (!dq.empty() && A[i] <= dq.front()) {
            poz.pop_front();
            dq.pop_front();
        }
        poz.push_back(i);
        dq.push_back(A[i]);
    }
    sum += dq.front();
    for (int i = k + 1; i <= n; ++i) {
        cin >> A[i];
        if (i - poz.front() >= k) {
            dq.pop_front();
            poz.pop_front();
        }

        while (!dq.empty() && A[i] <= dq.front()) {
            poz.pop_front();
            dq.pop_front();
        }
        poz.push_back(i);
        dq.push_back(A[i]);
        sum+=dq.front();
    }
    cout << sum;
    printf("\nTime taken: %.2fs\n", (double) (clock() - tStart) / CLOCKS_PER_SEC);
}