#include <fstream>

using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");

const int mxN = 5e6 + 1;
int valMin[mxN], n, k;

int minim(int a, int b){
    if(a < b)
        return a;
    return b;
}

void precompute(){
    for(int i = k; i >= 2; i--)
        valMin[i] = valMin[i - 1];
}

void compute(){
    for(int i = 2; i <= k; i++)
        valMin[i] = minim(valMin[i], valMin[1]);
}

int main(){
    int ans = 0;
    fin >> n >> k;
    for(int i = k; i >= 1; i--)
        fin >> valMin[i];
    compute();
    ans += valMin[k];

    for(int i = k + 1; i <= n; i++){
        precompute();
        fin >> valMin[1];
        compute();
        ans += valMin[k];
    }

    fout << ans;
    return 0;
}