#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

deque<long long> A;
int K, N, x, minim = 1000001, min_sum = 0;

int main()
{
    fin>>N>>K;
    for(int i = 0; i<N; i++)
    {
        fin>>x;
        A.push_back(x);
    }

    for(int i = 0; i<N-K+1; i++)
    {
        for(int j = 0; j<K; j++)
        {
            if(A[i+j] < minim)
                minim = A[i+j];
        }
        min_sum += minim;
        minim = 1000001;
    }

    fout<<min_sum;

    return 0;
}