#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int64_t a[5000001],s;
int64_t n,k,x=20000000;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>a[i];
    for(int i=1;i<=n;i++)
    {
        for(int j=i;j<i+k;j++)
        {
            int64_t y=a[j];
            x=min(x,y);
        }
        s+=x;
        x=20000000;
    }
    g<<s;
    return 0;
}