#include <fstream>
#include <deque>
#include <climits>
#define MARK 10000001

using namespace std;

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

int v[5000010];

int main() {
    int n, k;
    long long sum = 0;
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        fin >> v[i];
    }
    for (int i = 0; i < n - k + 1; ++i) {
        int min = MARK;
        for (int j = 0; j < k; ++j) {
            if (v[i + j] < min) {
                min = v[i + j];
            }
        }
        if (min != MARK) {
            sum += min;
        }
    }
    fout << sum << "\n";
    return 0;
}

/*
#include <fstream>
#include <deque>
#include <climits>
#define MARK 10000001

using namespace std;

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

int main() {
    deque<int> d;
    int n, k, currentValue, min = INT_MAX, pos = 0;
    long long sum = 0;
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        fin >> currentValue;
        d.push_back(currentValue);
    }
    // don't forget about the case where there aren't enough k numbers
    while (d[pos] != MARK  && d[k - 1] != MARK) {
        if (d[pos] < min) {
            min = d[pos];
        }
        if (pos == k - 1) {
            d.push_back(MARK);
            d.push_back(min);
            d.pop_front();
            min = INT_MAX;
            pos = -1;
        }
        ++pos;
    }
    while (d.front() != MARK) {
        d.pop_front();
    }
    for (int i = 0; i < d.size(); ++i) {
        if (d[i] != MARK) {
            sum += d[i];
        }
    }
    fout << sum;
    return 0;
}
*/