#include <iostream>
#include <queue>
#include <fstream>
#include <cstring>
#include <stack>
#define N_MAX 5000005
#define MOD 666013
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n,k;
int main()
{
    in >> n >> k;
    int el;
    long long sum=0;
    deque<pair<int,int>> d;
    for (int i = 0; i < n; i++) {
        in >> el;
        while (!d.empty() && d.back().first >= el) {
            d.pop_back();
        }
        d.push_back({ el, i});
        if (i < k-1)continue;
        while (!d.empty() && d.front().second < i - k + 1) {
            d.pop_front();
        }
        int minim = d.front().first;
        sum += minim;
    }
    out << sum;
    return 0;
}