#include <fstream>
#include <queue>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
typedef long long ll;
deque<pair<ll,ll> > dq;
int main()
{
    ll n,k,a;
    cin>>n>>k;
    for(ll i=1;i<=k;++i)
    {
        cin>>a;
        while(!dq.empty() and dq.back().first>=a)
            dq.pop_back();
        dq.push_back({a,i});
    }
    ll ans=dq.front().first;
    for(ll i=k+1;i<=n;++i)
    {
        cin>>a;
        if(dq.front().second==i-k)
            dq.pop_front();
        while(!dq.empty() and dq.back().first>=a)
            dq.pop_back();
        dq.push_back({a,i});
        ans+=dq.front().first;
    }
    cout<<ans<<'\n';
    return 0;
}