#include<iostream>
#include<fstream>
using namespace std;
long v[5000000],k;
int minim(long x)
{
    long min=v[x],i;
    for(i=x+1;i<x+k;i++)
        if(v[i]<min)
            min=v[i];
    return min;
}
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    long n ,i,s=0;
    f>>n>>k;
    for(i=1;i<=k;i++)
        f>>v[i];
    s=s+minim(1);
    for(i=k+1;i<=n;i++)
    {
        f>>v[i];
        if(v[i]<minim(i-k))
            s=s+v[i];
        else
            s=s+minim(i-k+1);
    }
    g<<s;
    return 0;
}