#include <fstream>

using namespace std;

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

long long s;
int n,k,st,dr,i,a[5000005],c[5000005];

int main()
{
    fin >> n >> k;
    st=1;
    dr=0;
    for (i=1;i<=n;i++)
    {
        fin >> a[i];
        while (st<=dr && a[i]<=a[c[dr]]) dr--;
        dr++;
        c[dr]=i;
        if (c[st]==i-k) st++;
        if (i>=k) s+=a[c[st]];
    }
    fout << s;

    return 0;
}