#include <deque>
#include <fstream>
#define ll long long
#define f first
#define s second
using namespace std;

deque<pair<int,int> > d;
int n,c,k;
ll ans;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(int i=0;i<n;i++) {
        if(!d.empty()&&i>=k)
            ans+=d.front().f;
        if(!d.empty()&&d.front().s<=i-k)
            d.pop_front();
        fin>>c;
        while(!d.empty()&&d.back().f>c)
            d.pop_back();
        d.push_back({c,i});
    }
    ans+=d.front().f;
    fout<<ans;
    return 0;
}