#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque <int> d;
int n,k,i,a[5000000];
long long int s=0;

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