#include <bits/stdc++.h>
using namespace std;

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

const int nmax=5e6+3;
int n,k,v[nmax];
long long s;

void read(){
in>>n>>k;
for(int i=1;i<=n;i++)
in>>v[i];
}

void solve(){
deque<int>dq;

for(int i=1;i<=n;i++)
{
  while(!dq.empty()&&v[i]<=v[dq.back()])
    dq.pop_back();

   dq.push_back(i);

   if(i-k==dq.front()) dq.pop_front();

   if(i>=k) s=s+v[dq.front()];

}

out<<s;
}

int main(){
read();
solve();

return 0;
}