#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int n,v[5000001],k;
long long sol;
deque<int>D;
int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++)
        in>>v[i];
    for(int i=1;i<=n;i++)
    {
        while(!D.empty() && v[D.back()]>v[i])
        D.pop_back();
        D.push_back(i);
        if(k==i-D.front())D.pop_front();
        if(i>=k)sol+=v[D.front()];
    }
    out<<sol;
    return 0;
}