#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in"); ofstream g("deque.out");
deque <int> Q;
int n,k,a[5000001];
long long s;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
    {
        f>>a[i];
        while(!Q.empty() and a[Q.front()]>a[i]) Q.pop_front();
        Q.push_front(i);
        if(!Q.empty() and (i-Q.back())>=k)Q.pop_back();
        if(i>=k)s+=a[Q.back()];
    }
    g<<s;
    return 0;
}