#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; }