#include <fstream>
#define NMAX 5000010

using namespace std;

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

int n,k,i,v[NMAX],p[NMAX],a,b;
long long s;

int main()
{fin>>n>>k;
for(i=1;i<=n;i++)
fin>>v[i];
b=0;a=1;
    for(i=1;i<=n;i++)
    {while(a<=b && v[i]<=v[p[b]])b--;
    p[++b]=i;
    if(p[a]==i-k) a++;
    if(i>=k)s+=v[p[a]];
    }
    fout<<--s;
    return 0;
}