#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    int n, k;
    ifstream in("deque.in");
    ofstream out("deque.out");
    in >> n >> k;
    int v[n], suma = 0;
    for(int i = 0; i < n; i++)
        in >> v[i];
    int st = 0, dr = k, minn = v[0];
    for(int i = st; i < dr; i++)
        if(minn > v[i])
            minn = v[i];
    suma += minn;
    while(dr < n) {
        dr++;
        st++;
        minn = v[st];
        for(int i = st; i < dr; i++)
            if(minn > v[i])
                minn = v[i];
        suma += minn;
    }
    out << suma;
    return 0;
}