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

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

int main() {
int n, k;
fin>>n>>k;
vector<int> a(n+1);
for (int i=1; i<=n; ++i) fin>>a[i];
deque<int> q;
for (int i=1; i<=k; ++i) {
while (!q.empty() && a[q.back()] >= a[i]) q.pop_back();
q.push_back(i);
}
long long S = a[q.front()];
for (int i=k+1; i<=n; ++i) {
while (!q.empty() && q.front() <= i-k) q.pop_front();
while (!q.empty() && a[q.back()] >= a[i]) q.pop_back();
q.push_back(i);
S += a[q.front()];
}
fout<<S;
}