#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

deque <int> d;

int i,n,k,a[5000001];
long long s;

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