#include <fstream>
#include <deque>
#include <algorithm>
#define INF (2000000000)
using namespace std;

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

deque<int> d;

int n,i,k,v[5000200];
long long s;


int main()
{
    in>>n>>k;
    for(i=1; i<=n; i++)
    {
        in>>v[i];
        while(!d.empty() && v[i] <= v[d.back()])
            d.pop_back();
        d.push_back(i);
        if(d.front() == i-k)
            d.pop_front();
        if(i>=k)
            s+=v[d.front()];
        
    }
    out<<s;

    return 0;
}