#include<iostream>
#include<fstream>
#define ll long long

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    ll i,sum=0,n,k,min,j;
    f>>n>>k;
    ll a[n+1];
    for(i=1;i<=n;i++)
        f>>a[i];
    for(i=1;i<=n-k+1;i++)
    {min =a[i];
        for(j=i+1;j<=k+i;j++)
            if(min>a[j])
            min=a[j];
        sum+=min;
    }
    g<<sum;
    return 0;
}