#include <fstream>
#include <deque>
#define maxi 5000005

using namespace std;

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

deque <int> d;
int n,k,v[maxi];
long long suma;

int main()
{
    fi>>n>>k;
    for(int i=1; i<=n; i++)
        fi>>v[i];
    for(int i=1; i<=n; i++)
    {
        if(i<k)
        {
            while(!d.empty() && v[i]<=v[d.back()])
                d.pop_back();
            d.push_back(i);
        }
        else
        {
            while(!d.empty() && v[i]<=v[d.back()])
                d.pop_back();
            d.push_back(i);
            if(d.front() <= i-k)
                d.pop_front();
            suma+= v[d.front()];
        }
    }
    fo<<suma;
    return 0;
}

/*
push_front
pop_front
push_back
pop_back
*/