#include <fstream>
#include <deque>
#define int long long

using namespace std;

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

deque <pair<int,int>> dq;

signed main()
{
    int n,k,sum=0;
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        int nr;
        cin>>nr;
        while(!dq.empty() && dq.back().second>=nr) dq.pop_back();
        dq.push_back({i,nr});
        while(!dq.empty() && dq.front().first<=i-k) dq.pop_front();
        if(i>=k) sum+=dq.front().second;
    }
    cout<<sum<<endl;
    return 0;
}