#include <fstream>
#define nMax 5000001

using namespace std;

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

int n, k;
int v[nMax], deque[nMax];
long long Sol;
int read()
{
    fin>>n>>k;

    for(int i=1; i<=n; i++)
        fin>>v[i];
}

void solve()
{
    int st=1, dr=0;

    for(int i=1; i<=n; i++)
    {
        if(deque[st]==i-k)
            st++;

        while(v[i]<=v[deque[dr]] && dr>=st)
            dr--;

        deque[++dr]=i;

        if(i>=k)
            Sol+=v[deque[st]];
    }
}

void write()
{
    fout<<Sol;
}

int main()
{
    read();
    solve();
    write();
}