#include<fstream>
#include<deque>
#define maxn 5000010
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k;
int v[maxn];
deque<int> deck;
long long s;

int main(){
f>>n>>k;
for (int i=1;i<=n;i++)
f>>v[i];
for(int i=1;i<=n;i++){
while(deck.size()!=0&&v[i]<=v[deck.back()])
deck.pop_back();

deck.push_back(i);

if(deck.front()==i-k)
deck.pop_front();

if(i>=k) s+=v[deck.front()];
}

g<<s<<'\n';
return 0; 
}