#include<fstream>
#define NMAX 5000010
using namespace std;
int V[NMAX], Deque[NMAX], P,U,N,K;
long long S;
int main()
{
ifstream f("Deque.in");
ofstream g("Deque.out");
int i;
f>>N>>K;
for(i=1;i<=N;i++)
f>>V[i];
P=1;U=0;
for(i=1;i<=N;i++)
{
while((P<=U)&& V[i]<=V[Deque[U]])
U--;
Deque[++U]=i;
if(Deque[P]==i-K) P++;
if(i>=K) 
S+=V[Deque[P]];
 }
g<<S;
return 0; }