//Problema: http://infoarena.ro/problema/deque

#include <stdio.h>
#include <deque>
using namespace std;

//Global data
deque<long long> Deque;
deque<long long> Mins;
long long N, K, Aux, Min;
long long S=0;

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);

    scanf("%lld%lld",&N,&K);

    for(int i=0; i<N; i++)
    {
        scanf("%lld", &Aux);
        Deque.push_back(Aux);
    }

    while(Deque.size()>2)
    {
        Min = Deque.front();

        Deque.pop_front();

        for(int i=0; i<K-1; i++)
        {
            if(Min>Deque[i])
                Min = Deque[i];
        }

        S+=Min;

    }

    printf("%lld",S);

	return 0;
}