#include <fstream>
#include <deque>
#define NMAX 5000002
using namespace std;

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

int n, k;
deque<int>T;

long long s;
long long a[NMAX];

int main()
{
    f>>n>>k;
    for(int i=0; i<n; i++){
        f>>a[i];
        while(!T.empty() && a[i] <= a[T.back()])
            T.pop_back();
        T.push_back(i);
        if(T.front()<i-k+1){ /// 21  4 5 6 7
            T.pop_front();
        }
        if(i>=k-1){
            s+=a[T.front()];
        }
    }
    g<<s;
    return 0;
}