#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;

using namespace __gnu_pbds;


using ll = long long;
using ull = unsigned long long;
using ld = long double;

template<class __set_element_type>
using gnu_set= tree<__set_element_type, null_type,less<__set_element_type>, rb_tree_tag,tree_order_statistics_node_update>;
template<class __key_type, class __val_type>
using gnu_map = tree<__key_type, __val_type,less<__key_type>, rb_tree_tag,tree_order_statistics_node_update>;

#define ios ios::sync_with_stdio(0); cin.tie(0)


const ll oo = 1e18;
const ll MOD = 1e9 + 7;

int n, k;

int main() {
    ios;
    cin >> n >> k;
    vector<ll> vec(n);
    vector<bool> touched(n, false);
    for(auto &v: vec)
        cin >> v;

    vector<ll> sums;
    for(int i = 0; i < n; i++) {
        ll sum = 0;
        if(touched[i])
            continue;
        for(int j = i; j < n; j += k) {
            sum += vec[j];
            touched[j] = true;
        }
        sums.push_back(sum);
        
    }
    sort(begin(sums), end(sums));
    ll result = 0;
    for(auto s: sums)
        result += s;
    result -= sums.back();
    cout << result;
}