#include <bits/stdc++.h>
#define prim 123457
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int a[5000005],n,k;
deque<int>minim;
long long sol;
int main()
{
    int i,x;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
    for(i=1;i<=k;i++)
    {
         x=a[i];
        while(!minim.empty() and a[minim.back()]>x)
            minim.pop_back();
        minim.push_back(i);
    }
    sol+=a[minim.front()];
    for(i=k+1;i<=n;i++)
    {
        x=a[i];
        while(!minim.empty() and a[minim.back()]>x)
            minim.pop_back();
        minim.push_back(i);
      if(i-minim.front()>=k)
        minim.pop_front();
        sol+=a[minim.front()];
    }
    fout<<sol<<"\n";
    fin.close();
    fout.close();
    return 0;
}