#include <fstream>

using namespace std;
int n, i, minim, j, s, v[5000003], k;
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for (i = 1;i <= n;i++)
        fin>>v[i];
    for (i = 1;i <= n - k + 1;i++){
        minim = 200000000;
        for (j = i;j <= i + k - 1;j++){
            if(v[j] < minim)
                minim = v[j];
        }
        s += minim;
    }
    fout<<s;
    return 0;
}