#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int sir_numere[5000001], deq[5000001];
int main()
{
    int N, i, K, st=1, dr=0;
    long long suma=0;
    in >> N >> K;
    for(i = 1; i <= N; i++)
        in >> sir_numere[i];
    for(i = 1; i <= N; i++)
    {
        while (st <= dr && sir_numere[i] <= sir_numere[deq[dr]])
            dr--;
        deq[++dr] = i;
        if (deq[st] == i-K) st++;
        if (i >= K)
            suma += sir_numere[deq[st]];
    }
    out << suma;
    return 0;
}