#pragma GCC optimize("O2")
#include <bits/stdc++.h>
using namespace std;

#define ll     long long
#define test   int tt; cin>>tt; while(tt--)
#define ff     first
#define ss     second
#define pb     push_back
#define ppb    pop_back
#define pf     push_front
#define ppf    pop_front

int dp[5001][5001];

ll int cal(vector<int> &zero_pos, vector<int> &one_pos, int i, int j)
{
    if(i==zero_pos.size() && j<one_pos.size())
        return INT_MAX;

    if(j==one_pos.size())
        return 0;

    if(dp[i][j]!=-1)
        return dp[i][j];

    ll int x=fabs(zero_pos[i]-one_pos[j]);

    return dp[i][j]=min(cal(zero_pos, one_pos, i+1, j),
                        x+cal(zero_pos, one_pos, i+1, j+1));
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    fill(dp[0], dp[0]+5001*5001, -1);

    int n;
    cin>>n;

    int arr[n];
    for(int i=0; i<n; i++)
        cin>>arr[i];

    vector<int> zero_pos, one_pos;

    for(int i=0; i<n; i++)
    {
        if(arr[i]==0)
            zero_pos.pb(i);
        else
            one_pos.pb(i);
    }

    cout<<cal(zero_pos, one_pos, 0, 0)<<endl;
}
