#include <iostream>
#include <fstream>
#include <deque>
#define MAXN 5000041
using namespace std;
ifstream f1("deque.in");
ofstream f2("deque.out");
int a[MAXN],n,k;
long long sum;
deque <int> d;
int main()
{
    f1>>n>>k;
    for(int i=1;i<=n;i++) f1>>a[i];
    for(int i=1;i<=n;i++){
        if(i<k){
            while(!d.empty() && a[i]<a[d.back()])
                d.pop_back();
            d.push_back(i);
        }
        else{
            while(!d.empty() && a[i]<a[d.back()])
                d.pop_back();
            d.push_back(i);
            if(d.front()<=i-k)
                d.pop_front();

            sum+=a[d.front()];
        }
    }
    f2<<sum;
    return 0;
}