#include<fstream>
using namespace std;
int deque[5000010],v[5000010],i,n,p,u,k;
long long sol;
int main()
{
ifstream f("deque.in");
ofstream g("deque.out");
f>>n>>k;
for(i=1;i<=n;i++) f>>v[i];
p=u=1;

for(i=1;i<=n;i++)

 { while(i-k>=deque[p] && p<=u) p++;

   while(v[i]<v[deque[u]] && p<=u) u--;

   deque[++u]=i;

   if(i>=k) sol+=(long long)v[deque[p]];
 }
g<<sol;
f.close();
g.close();
return 0;
}