#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int toate_numerele[5000000];
int minim(int v[], int i, int k) ///minim(v,i,i+K-1)
{
    int mini;
    mini=v[i];
    for(int j = i; j <= k; j++)
    {
        if(v[j] < mini)
            mini = v[j];
    }
    return mini;
}
int main()
{
    int N, K, i, s = 0;
    in >> N >> K;
    for(i = 0; i < K; i++)
    {
        in >> toate_numerele[i];
    }
    for(i = K; i <= N; i++)
    {
        in >> toate_numerele[i];
        s += minim(toate_numerele, i-K, i-1);
        ///out<<"s= "<<s<<'\n';
        ///out<<"i-K= "<<i-K<<" i-1= "<<i-1<<'\n';
    }
    out << s;
    return 0;
}