#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

int v[5000002];


int main(){
    long long n,i,j,k,S,vmin;
    fin>>n;
    fin>>k;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    S=0;
    for(i=1;i<=n-k+1;i++)
    {   vmin=v[i];
        for(j=i+1;j<=n-i+1;j++)
            if(v[j]<vmin) vmin=v[j];
        S=S+vmin;
    }
    fout<<S;
    fin.close();
    fout.close();
    return 0;
}