#include <algorithm>
#include <fstream>
#include <vector>

int main(){
    int n, k;
    std::ifstream in("deque.in");
    long long int result = 0;
    in>>n>>k;
    std::vector<int> last(k, 0);
    for(int x = 0;x<k;x++){
        in>>last[x];
    }
    result+=*std::min_element(last.begin(), last.end());
    int tail_ptr = 0, last_tail;
    for(int x = k;x<n;x++){
        last_tail = tail_ptr;
        in>>last[tail_ptr];
        tail_ptr++;
        if(tail_ptr==k)tail_ptr = 0;
        result+=*std::min_element(last.begin(), last.end());
    }
    std::ofstream("deque.out")<<result;
}