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

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k,stanga,dreapta;
    int v[50000];
    long long s=0;
    fin>>n>>k;
    int dq[50000];
    for(int i = 1; i <= n; i++) {
        fin>>v[i];
    }
    stanga=1;
    dreapta=0;
    for(int i = 1; i <= n; i++) {
        while(stanga<=dreapta && v[i] <= v[dq[dreapta]])
        {
            dreapta--;
        }
        dreapta++;
        dq[dreapta]=i;
        if(i >= k) {
            s += v[dq[stanga]];
            if(dq[stanga] == i - k + 1) {
                stanga++;
            }
        }
    }
    fout<<s;

    return 0;
}