# include <fstream>
# include <iostream>
# include <deque>
# include <vector>
using namespace std;
ifstream fi("deque.in");
ofstream fo("deque.out");
vector <int> s;
deque <int> p;
int main(void)
{
    int n,k;
    long long M=0;
    fi>>n>>k;
    s.resize(n+5);
    for (int i=1;i<=n;++i) fi>>s[i];
    for (int i=1;i<=n;++i)
    {
        while (!p.empty() && s[i]<=s[p.back()]) p.pop_back();
        p.push_back(i);
        if (p.front() == i-k) p.pop_front();
        if (i>=k) M+=s[p.front()];
    }
    fo<<M<<"\n";
}