#include <deque>
#include <iostream>
#include <fstream>
#define nmax 5000005
using namespace std;

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

int n, k;
deque <int> d;
int A[nmax];
long long S;

void solve() {
    int i;
    fin >> n >> k;
    for (i = 1; i <= n; i++) {
        fin >> A[i];
        while (!d.empty() && A[i] <= A[d.back()]) d.pop_back();
        d.push_back(i);
        if (i - d.front() >= k) d.pop_front();
        if (i >= k) S += A[d.front()];
    }
    fout << S << "\n";
}

int main() {
    solve();
    fin.close();
    fout.close();
    return 0;
}