#include <fstream>
#include <deque>
#define int long long
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, i, j, a[5000005], ans;
deque <int> q;
signed main()
{
    fin>>n>>k;
    for(i=1; i<=n; i++)
        fin>>a[i];
    q.push_back(1);
    for(i=2; i<=k; i++)
    {
        while(!q.empty() && a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    ans=a[q.front()];
    for(i=k+1; i<=n; i++)
    {
        if(q.front()<i-k+1)
            q.pop_front();
        while(!q.empty() && a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
        ans+=a[q.front()];
    }
    fout<<ans;
    return 0;
}