#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int main() {

    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int n, k;
    scanf("%d%d", &n, &k);
    int i,j;
    long c[n], cost[k+1];
    for(i=0;i<n;i++)
        scanf("%ld", &c[i]);
    for(j=0;j<k;j++){
        cost[j]=0;
        for(i=j;i<n; i+= 2*k){
        cost[j]+= c[i];
    }
        //printf("%ld", cost[j]);
    }
    long  min = cost[0];
    for(i=0;i<k;i++)
        if(cost[i]<min)
        min= cost[i];
    
    printf("%ld", min);
    return 0;
}