#include <iostream>
#include <fstream>

#define LLONG_MAX 9223372036854775807

int minim(long long* v, unsigned int start, unsigned int& k) {
    long long m = LLONG_MAX;
    for (unsigned int i = start; i < start + k; i++) {
        if (v[i] < m)
            m = v[i];
    }
    return m;
}

int main()
{
    std::ifstream f("deque.in");
    std::ofstream g("deque.out");

    unsigned int n, k;
    f >> n >> k;
    long long* a = new long long[n];
    for (unsigned int i = 0; i < n; i++) {
        f >> a[i];
    }

    int s = 0;
    for (unsigned int i = 0; i < n - k + 1; i++) {
        s += minim(a, i, k);
    }

    g << s;

    delete[] a;
}