#include <fstream>
#include <deque>
using namespace std;
#define maxn 5000000
ifstream cin("deque.in");
ofstream cout("deque.out");

int n, k;
int a[maxn];
long long s;
int main()
{

    deque <int> d;

    cin>>n>>k;

    for(int i=0; i<n; i++)
        cin>>a[i];

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