#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,v[5000009],minn,sol[5000009],i,j;
long long s;
int main()
{
    int inc=1,fin=0;
    f>>n>>k;
    for (i=1;i<=n;i++)
        f>>v[i];

    s=0;
    for (i=1;i<=k;i++)
    {
        while(inc<=fin&&v[i]<sol[fin])
            fin--;
        sol[++fin]=v[i];
    }
    s+=sol[inc];
    for(i=1;i<=n;i++)
    {
        while(inc<=fin&&v[i]<sol[fin])
            fin--;
        sol[++fin]=v[i];
        if(sol(inc)==v[i-k])
            inc++;
        s+=sol[inc];
    }
    g<<s;
    f.close();
    g.close();
    return 0;
}