#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

 int A[5000001],N,K,st=0,dr=0,i,S=0,mn;
int main()
{

    fin>>N>>K;
    dr=st+K-1;
    for(i=0;i<N;i++)
        fin>>A[i];
    while(dr<=i-1)
    {
        mn=A[st];
        for(int j = st;j<=dr;j++)
            if(A[j]<mn)
                mn=A[j];
        S=S+mn;
        st++;
        dr++;
    }
    fout<<S;

}