#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int>d;
int a[5000001];
int n,k,i;
long long s;
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()];
}
g<<s;
    return 0;
}