#include <iostream>
#include <fstream>
#include <algorithm>
#include<bits/stdc++.h>
#include<vector>
#include<stack>
#include<queue>
using namespace std;
long long minim=100000000;
ifstream in("deque.in");
ofstream out("deque.out");
long n,i,j,k,nr,v[5000001],sum=0;

int main()
{
    in>>n>>k;
    for(i=0; i<n; i++)
        in>>v[i];
    for(i=0; i<=n-k; i++)
    {
        minim=v[i];
        for(j=i; j<i+k; j++)
            if(v[j]<minim)
               minim=v[j];
        sum+=minim;
    }
    out<<sum;
}