#include <fstream>
#include <deque>
#include <vector>
using namespace std;
deque <int> d;
int i,n,k,b,a[5000005];

long long s;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    f>>n>>k;
    for (i=1;i<=n;i++)
    {
        f>>a[i];
        while (!d.empty() && a[d.back()]>=a[i]) d.pop_back();
        d.push_back(i);
        if (i-k==d.front()) d.pop_front();
        if (i>=k) s+=a[d.front()];
    }
    g<<s;
    return 0;
}