#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

deque <int> d;
int n,k,x;
int v[5000001];



int main()
{  int i; long long s=0;
   fin>>n>>k;
   for (i=1;i<=n;++i) fin>>v[i];
   for (i=1;i<=n;++i)
       { while (!d.empty() && v[d.back()]>=v[i])
                      d.pop_back();
         d.push_back(i);
         if (i-k==d.front()) d.pop_front();
         if(i>=k) s+=v[d.front()];
       }
   fout<<s;

   return 0;
}