#include <fstream>
#include <deque>
#define mv 5000009
#define LL long long
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,A[mv];
deque < int > dq;
int main()
{
    LL sum = 0;
    f >> n >> k;
    for(int i=1; i<=n; i++) f >> A[i];

    for(int i=1; i<=n; i++)
    {
        while(!dq.empty() && A[i] <= A[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front() == i-k) dq.pop_front();
        if(i >= k) sum += A[dq.front()];
    }

    g << sum << '\n';
    g.close();
    return 0;
}