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

using namespace std;

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

ll n,m,i,a,sum=0;
deque <pair<ll,ll> > v;
int main()
{
    cin>>n>>m;
    for (i=1;i<=n;++i)
    {
        cin>>a;
        if (!v.empty() && a<=v[0].first)
        {
            v.clear();
            v.push_back({a,i});
            if (i>=m) sum+=a;
        }
        else
        {
            while (!v.empty() && v.back().first>a) v.pop_back();
            v.push_back({a,i});
            if (i>=m)
            {
                while (v[0].second<=i-m) v.pop_front();
                sum+=v[0].first;
            }
        }
    }

    cout<<sum;
    return 0;
}