#include <fstream>
#include <queue>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
struct RaresHolmes{
int val,poz;
}a;
long long n, k,smin,i,capat1,capat2;
deque <RaresHolmes> q;
int main()
{
    fin >> n >> k;
    for(int i = 1; i <= k; i++)
    {
        fin >>a.val;
        a.poz=i;
        while(!q.empty()&&q.back().val>a.val)
            q.pop_back();
        q.push_back(a);
    }
    smin=q.front().val;
    capat1=1;capat2=k;
    for(i=k+1;i<=n;i++)
    {
        fin>>a.val;a.poz=i;capat1++;capat2++;
        if(q.front().poz<capat1)
            q.pop_front();
        while(!q.empty()&&q.back().val>a.val)
            q.pop_back();
        q.push_back(a);
        smin+=q.front().val;
    }
    fout<<smin<<'\n';
    return 0;
}