#include <fstream>
#include <deque>

using namespace std;

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

long long v[5000001];
deque<int>dq;

int main()
{
    long long s;
    int n,k,i;
    cin>>n>>k;
    s=0;
    for(i=1;i<=n;i++){
        cin>>v[i];
        while(!dq.empty() && v[i]<v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k){
            if(!dq.empty() && i-k+1>dq.front())
                dq.pop_front();
            s=s+v[dq.front()];
        }
    }
    cout<<s;
    return 0;
}