#include <cstdlib>
#include <fstream>
#include <iostream>
using namespace std;

#define maxn 5000010

ifstream fin("deque.in");
ofstream fout("deque.out");
int a[maxn];
#define inf 1000000000
int main() {
    
    int N,K,i,j,MI,x,S=0;
    fin>>N>>K;
    j=K;
     for (i = 1; i <= N; i++)
         fin>>a[i];
    
    while(j<=N){
        MI = inf;
        for(i=j-K+1;i<=j;++i){
            if(a[i] < MI){
                MI = a[i];
                
            }
        }
        S = S + MI;
        j++;
    }
    fout<<S;
    
    return 0;
}