#include<fstream>
#define nmax 5000010
using namespace std;
ifstream f("deque.in"); ofstream g("deque.out");
int n,k,st,dr,i,a[nmax],D[nmax];
long long s;
int main()
{   f>>n>>k;
    for(i=1;i<=n;++i) f>>a[i];
    st=1; dr=0;
    for(i=1;i<=n;++i)
    {   while(st<=dr && a[i]<=a[D[dr]]) dr--;
        D[++dr]=i;
        if(D[st]==i-k) st++;
        if(k<=i) s+=a[D[st]];
    }
    g<<s<<'\n'; g.close(); return 0;
}