#include<fstream>
using namespace std;
int v[5000000],dq[5000000],st=1,dr,k;

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

void dreapta(int i)
{
while((st<=dr)&&(v[dq[dr]]>=v[i]))
{
--dr;
}
}



inline void stanga(int i)
{
if(i-dq[st]==k)
++st;
}
 

 

int main()
{
int n,i;
long long s=0;
in>>n>>k;
for(i=1;i<=n;++i)
in>>v[i];
for(i=1;i<=k;++i)
{
dreapta(i);
dq[++dr]=i;
}
s=s+v[dq[st]];
for(;i<=n;++i)
{
stanga(i);
dreapta(i);
dq[++dr]=i;
s=s+v[dq[st]];
}

out<<s;
return 0;
}