#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,i,v[5000005],dq[5000005],dr,st,k;
long long s = 0;
int main()
{
    f>>n>>k;
    for(i=1;i<=n;i++) f>>v[i];
    st = 1;
    dr = 0;
    s = 0;
    for(i=1;i<=n;i++)
    {
        if(st<=dr and dq[st]==i-k) st++;
        while(st<=dr and v[i]<=v[dq[dr]]) dr--;
        dq[++dr] = i;
        if(i>=k) s+=v[dq[st]];
    }
    g<<s<<'\n';
    return 0;
}