#include<fstream>
#define maxim 5000010
using namespace std;
ifstream in ("deque.in");
ofstream out("deque.out");
int n,m,v[maxim],deque[maxim],front,back;
long long sol;

int main()
{
int i;
in>>n>>m;
for(i=1;i<=n;i++)
    in>>v[i];
front=1;
back=0;
for(i=1;i<=n;i++){
while (front<=back&&v[i]<=v[deque[back]])back--;
deque[++back]=i;
if(deque[front]==i-m) front++;
if(i>=m) sol=sol+v[deque[front]];
}
out<<sol<<'\n';
out.close();
in.close();
return 0;
}