#include <bits/stdc++.h>

using namespace std;

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

int n,k;
long long v[5000005];
long long int suma;

deque < long long int > Q;

int main()
{
    in>>n>>k;
    for(int i=1; i<=n; i++)
    {
        in>>v[i];
        while(!Q.empty() && v[i] <= v[Q.back()])
            Q.pop_back();
        Q.push_back(i);
        if(Q.front() <= i - k)
            Q.pop_front();
        if(i >= k)
            suma += v[Q.front()];
    }
    out<<suma;
    return 0;
}