#include <fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,a[5000001],st,dr,q[5000001];
long long s;
int main()
{   fin>>n>>k;
    for(int i=1;i<=n;i++)
        fin>>a[i];
        st=1,dr=0;
    for(int i=1;i<=n;i++)
    {
        while(st<=dr && a[i]<=a[q[dr]])
            dr--;
        q[++dr]=i;
        if(q[st]==i-k) st++;
        if(i>=k) s+=a[q[st]];
    }
    fout<<s;
    return 0;
}