#include <iostream>
#include <algorithm>
#include <math.h>
#include <vector>
#include <string>
#include <utility>
#include <stdio.h>
#include <queue>
#include <fstream>
#include <functional>
#include <cstdlib>
#include <map>
#include <set>
#include <bitset>
#include <string.h>

#define MAX_N 5000
#define INF 99999999
#define N_CHAR 130

using namespace std;

typedef pair<int, int> ii ;
typedef vector< ii >   vii ;
typedef vector<int> vi ;

int N, freccia[MAX_N],memo[MAX_N][MAX_N];

int dp(int start, int end){
    int count = 0;
    if(start >= end)
        return INF;
    if(memo[start][end]!=-1)
        return memo[start][end];

    for(int i=start;i<end;i++){
        if(i<(start+end)/2)
            count += abs(freccia[i]-0);
        else
            count +=abs(freccia[i]-1);
    }
    int sol = count;
    for(int i=start+2;i<=end-2;i+=2)
        sol = min(sol, dp(start,i) + dp(i, end));
    //cout <<start<<" "<<end<<" "<<sol<<endl;
    return memo[start][end] = sol;

}
int Gira(int N, int *freccia){
    memset(memo,-1,sizeof memo);
    return dp(0,N);
}
/*int main() {
    #ifdef EVAL
        freopen("input.txt","r",stdin);
        freopen("output.txt","r",stdout);
    #endif
        scanf("%d",&N);
        for(int i=0;i<N;i++)
            scanf("%d",freccia+i);
        //memset(memo, -1, sizeof memo);
        printf("%d",Gira(N, freccia));

    return 0;
}*/