#include <cstdio>
#include <algorithm>
using namespace std;

long long N, v[32001], ans, b0, b1, r, B0, B1, R;

int main(){

scanf("%d", &N);

for(int i = 1; i <= N; i++){
    scanf("%lld", &v[i]);
}

for(int i = 1; i <= N; i += 2){
    if(v[i]) b1++;
    else b0++;
}

for(int i = 2; i <= N; i += 2){
    if(v[i]) B1++;
    else B0++;
}

printf("%lld\n", min(b0 + B1, b1 + B0));

return 0;
}