#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <int> d;
long long s;
int n,k,i,v[5000005];
int main()
{
    f>>n>>k;

    for(i=1;i<=n;i++)
    {
        f>>v[i];
        while(!d.empty()&&v[d.back()]>=v[i])
            d.pop_back();
        d.push_back(i);
        if(i-d.front()==k) d.pop_front();
        if(i>=k) s+=v[d.front()];
    }
    g<<s;
    return 0;
}