#include <algorithm>
#include <iostream>
#include <fstream>
#include <vector>
#include <deque>

using namespace std;

int main() {
    // fstream fi("i.txt", ios::in);
    // fstream fo("o.txt", ios::out);

    fstream fi("deque.in");
    fstream fo("deque.out");
    
    int n, k;
    vector<long long> v;
    deque<long long> q;
    long long s=0;

    fi >> n >> k;
    v.resize(n);
    q.resize(k);

    for (int i=0; i < n; ++i) {
        fi >> v[i];
        if (i < k)
            q[i] = v[i];
    }
         
    int i = k;
    s += *min_element(q.begin(), q.end());
    while (i < n) {
        q.pop_front();
        q.push_back(v[i++]);
        s += *min_element(q.begin(), q.end());
    }

    fo << s;

    fo.close();
    fi.close();

    return 0;
}