#include <iostream>
#include <map>
#include <algorithm>
#include <vector>
#include <numeric>
#include <sstream>
#include <cmath>
#include <set>
#include <stack>
#include <iomanip>
#include <limits.h>
#include <queue>
#include <fstream>
#include <unordered_set>
#include <unordered_map>
#include <exception>
#include <string>

using namespace std;
fstream in_file;
fstream out_file;

int min(vector<int> vector)
{
    int min = INT_MAX;
    for(int nr : vector)
    {
        if (min > nr)
            min = nr;
    }
    return min;
}

vector<int> pop_front(vector<int> vector)
{
    vector.erase(vector.begin());
    return vector;
}


int main()
{
    in_file.open("deque.in", ios::in);
    out_file.open("deque.out", ios::out | ios::trunc);

    vector<int> nr;
    
    int N, K, x;
    long suma = 0;
    in_file >> N >> K;

    int i = 0;

    for (; i < K; i++)
    {
        in_file >> x;
        nr.push_back(x);
    }
    
    suma = suma + min(nr);

    for (; i < N; i++)
    {
        pop_front(nr);
        in_file >> x;
        nr.push_back(x);
        suma = suma + min(nr);
    }

    out_file >> suma;
    out_file.close();

    return 0;
}