#include <fstream.h>
#define nmax 5000005
ifstream fin("deque.in");
ofstream fout("deque.out");



long n,k,p,u, d[nmax],a[nmax];
long long s;


int main()
{fin>>n>>k;

for (long i=1;i<=n;i++)
fin>>a[i];

p=u=1;
d[1]=1;


for (i=2;i<=n;i++)
{while (p<=u && a[d[u]]>=a[i])
 u--;

 u++;
 d[u]=i;


if (d[p]==i-k) p++;

if (i>=k) s+=a[d[p]];


}



fout<<s;
fout.close();
return 0;
}