#include <iostream>
#include <fstream>
#include <deque>

using namespace std;
int findMin(deque<int> a){
    int re=a.front();
    for(auto x:a){
        if(x<re)re=x;
    }
    return re;
}
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n,k,x,rez=0;
    deque<int> d;
    in >> n;
    in >> k;
    for(int i=1;i<=k;i++){
            in >> x;
        d.push_back(x);
    }
    rez+=findMin(d);
    for(int i=1;i<=n-k;i++){
        in >> x;
        d.push_back(x);
        d.pop_front();
        rez+=findMin(d);
    }

    out << rez;
    return 0;
}