1 #include <bits/stdc++.h>
 2 
 3 using namespace std;
 4 
 5 #define REP(i,n)                for(int i(0); i <  (n); ++i)
 6 #define rep(i,a,b)              for(int i(a); i <= (b); ++i)
 7 const int N     =    100000      +       10;
 8 
 9 int a[N];
10 int n, k;
11 int ans;
12 int b[N], c[N];
13 int x;
14 
15 int main(){
16 
17     scanf("%d%d", &n, &k);
18     rep(i, 1, n) scanf("%d", a + i);
19     rep(i, 1, n){
20         x = i % k;
21         if (a[i] == 1) b[x]++; else c[x]++;
22     }
23 
24 
25     REP(i, k) ans += min(b[i], c[i]);
26     printf("%d\n", ans);
27     return 0;
28 
29 }