#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+3], suma = 0;
    for(int i = 1; i <= n; i++)
        in >> v[i];

    int st = 1, dr = k, minn = v[1];

    for(int i = st; i <= dr; i++)
        if(minn > v[i])
            minn = v[i];
    suma += minn;
    st = 2;
    dr = k + 1;
    while(dr <= n) {
        if(v[dr] < minn)
            minn = v[dr];
        else {
            minn = v[st];
            for(int i = st; i <= dr; i++)
                if(minn > v[i])
                    minn = v[i];
            }
        suma += minn;
        dr++;
        st++;
    }
    out << suma;
    return 0;
}