#include <iostream>
#include <fstream>
#include <deque>
const int NMAX=5000005;

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k;
deque<int>val;
long long s=0;
long long a[NMAX];

int main()
{
    fin>>n>>k;
    for(int i=0;i<n;i++)
    {
        fin>>a[i];
        while(!val.empty()&& a[i]<=a[val.back()]) val.pop_back();
        val.push_back(i);
        if(val.front()<i-k+1)
            val.pop_front();
        if(i>=k-1)
            s+=a[val.front()];
    }
    fout<<s;
    return 0;
}