#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const int inf = 2e9;
const int NMAX = 5000005;
int n,k,minim = inf,v[NMAX];
long long int suma;
deque<int>q;

int main(){
    int i,x,j;
    f >> n >> k;
    for(i = 1 ; i <= k ; i++){
        f >> x;
        q.push_back(x);
        minim = min(x,minim);
    }

    suma += minim;

    for(i = k + 1 ; i <= n ; i++){
        f >> x;
        q.push_back(x);
        minim = min(minim, x);
        if(q.front() == minim){
            q.pop_front();
            minim = inf;
            for(j = 0 ; j < q.size() ; j++)
                minim = min(minim, q[j]);
        }else
            q.pop_front();
        suma += minim;
    }

    g << suma;

    return 0;
}