#include <iostream>
#include <fstream>
using namespace std;
int minim(int v[],int start,int stop){
    int min=v[start];
    for(int i=start;i<stop;i++){
        if(min>v[i]) min=v[i];
    }
    return min;
}
int main()
{
    int n;
    int k;
    int suma=0;
    ifstream fin("deque.in");
    fin>>n>>k;
    int v[n];
    for(int i=0;i<n;i++){
        fin>>v[i];
    }
    for(int i=0;i<=n-k;i++){
        suma=suma+minim(v,i,i+k);
    }
    ofstream fout("deque.out");

    fout<<suma;
}