#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
deque<int>D;
int A[5000001];
int n,k,i;
long long S;
ifstream f("deque.in");
ofstream g("deque.out");
int main()
{f>>n>>k;
for(i=1;i<=n;i++)
{f>>A[i];
while(!D.empty()&&A[i]<=A[D.back()])
    D.pop_back();
D.push_back(i);
if(D.front()==i-k)
    D.pop_front();
if(i>=k)
    S+=A[D.front()];
}
f.close();
g<<S;
g.close();
    return 0;
}