#include <fstream>

using namespace std;

#define maxn 500001

long long int sum=0;
int i,n,k,st=1,dr=0,deq[maxn],v[maxn];

int main()
{
    fstream f("deque.in", ios::in);
    fstream g("deque.out", ios::out);
    f>>n>>k;
    for (i=1;i<=n;i++)
    {
        f>>v[i];
        while(dr>=st && v[i]<=v[deq[dr]])
            dr--;
        dr++;
        deq[dr]=i;
        if(deq[st]==i-k)
            st++;
        if(i>=k)
            sum+=v[deq[st]];
    }
    g<<sum;
    return 0;
}