#include <bits/stdc++.h>

 using namespace std;

 #define REP(i,n)                for(int i(0); i <  (n); ++i)

 #define rep(i,a,b)              for(int i(a); i <= (b); ++i)

 const int N     =          +       ;

 int a[N];

 int n, k;

 int ans;

 int b[N], c[N];

 int x;

 int main(){

     scanf("%d%d", &n, &k);

     rep(i, , n) scanf("%d", a + i);

     rep(i, , n){

         x = i % k;

         if (a[i] == ) b[x]++; else c[x]++;

     }

     REP(i, k) ans += min(b[i], c[i]);

     printf("%d\n", ans);

     return ;

 }