#include <fstream>
#include <queue>
using namespace std;

ifstream f("dequeue.in");
ofstream g("dequeue.out");

int n, m;
int v[5000010], dq[5000010];
int p, u;
long long sum;

int main()
{
    f>>n>>m;
    for(int i=1; i<=n; i++)
        f>>v[i];
    p=1, u=0;
    for(int i=1; i<=n; i++)
    {
        while(p<=u && v[i] <= v[dq[u]])
            u--;
        dq[++u]=i;
        if(dq[p]==i-m)
            p++;
        if(i>=m)
            sum+=v[dq[p]];
    }
    g<<sum;
    return 0;
}