#include <iostream>
#include <fstream>
#define N 5000001
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int a[N], deque[N], pr, ul;
int n, k;
long long s;

int main()
{
   int i, x, mini, j;
   fin >> n >> k;
   for(i = 1; i <= n; i++)
        fin >> a[i];
    for(i = 1; i <= n; i++)
    {
        while (pr <= ul && a[i] < a[deque[ul]])
            ul--;
        deque[++ul] = i;
        if(deque[pr] <= i - k)
            pr++;
        if(i >= k) s+= a[deque[pr]];
    }
    fout << s;
    return 0;
}