#include<fstream>
#include<queue>
#define maxN 5000001
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

deque<int>q;
int a[maxN];
int64_t sol;
int n,k;
void citire()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>a[i];

}
void solve()
{
    for(int i=1;i<=n;i++)
    {
        while(!q.empty() && a[i] < a[q.back()]  ) q.pop_back();
        q.push_back(i);
        if( q.front() == i-k ) q.pop_front();
        if ( i >= k ) sol+=a[q.front()];
    }
    g<<sol;
}
int main()
{
    citire();
    solve();
    return 0;
}