#include <fstream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

#define lim 5000000
int ini[lim], d[lim];
long long n,k,st=0,sum=0,dr=-1;

int main()
{
    fin>>n>>k;
    for (int i=0; i<n; i++)
    {
        fin>>ini[i];
        while (st<=dr && d[st]==i-k) st++;
        while (st<=dr && ini[i]<=ini[d[dr]]) dr--;
        d[++dr]=i;
        if (i>=k-1)
            sum += ini[d[st]];
    }
    fout<<sum;
    return 0;
}