#include <fstream>
#include <deque>
#include <vector>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

deque<int>v;

int main()
{
    int n,k;
    long long ans=0;
    in>>n>>k;
    vector<int>nr(n+1);
    for(int i=1;i<=n;i++){
        in>>nr[i];
        while(!v.empty() && nr[i]<nr[v.back()])
            v.pop_back();
        v.push_back(i);
        if(v.front() <= i-k)
            v.pop_front();
        if(i>=k)
            ans+=nr[v.front()];
    }
    out<<ans;
}