#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int main() {
    int n,k,x;
    f>>n>>k;
    int i,j;
    vector<int>v;
    while (f>>x)
    {
      v.push_back(x);

    }
    int suma = 0;
    for(i = 0;i<v.size()-k+1;i++) {
        int mn = 99999999;
        for (j = i; j < i + k; j++)
            if(mn>v[j])
                mn = v[j];
        suma += mn;
    }
    g<<suma;


  f.close();g.close();
}