#include <fstream>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,a[5000002],sol[5000002],k,st,dr;
long long s;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
    {
        f>>a[i];
    }
    dr=1;
    st=0;
    for(int i=1;i<=n;i++)
    {
        while(dr<=st && a[i]<=a[sol[st]])
        {
            st--;
        }
        sol[++st]=i;
        if(sol[dr]==i-k)dr++;
        if(i>=k)s=s+a[sol[dr]];
    }
    g<<s<<'\n';
    return 0;
}