#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;

const int MAX_N = 5050;
const int INF = (int)1e9;

int n;
int a[MAX_N];
int dp[MAX_N][MAX_N];
int mn[MAX_N][MAX_N];
vector<int> people, seats;

int main() {
  for (int i = 0; i < MAX_N; ++ i) {
    for (int j = 0; j < MAX_N; ++ j) {
        dp[i][j] = INF;
        mn[i][j] = INF;
    }
  }
  cin >> n;
  for (int i = 0; i < n; ++ i) {
    cin >> a[i];
    if (a[i]) {
      people.push_back(i);
    } else {
      seats.push_back(i);
    }
  }
  if (people.size() == 0) {
    cout << 0 << endl;
    return 0;
  }
  int ans = INF;
  for (int i = 0; i < seats.size(); ++ i) {
    dp[0][i] = abs(people[0] - seats[i]);
    if (i > 0) {
      mn[0][i] = min(mn[0][i - 1], dp[0][i]);
    } else {
      mn[0][i] = dp[0][i];
    }
  }
  for (int i = 1; i < people.size(); ++ i) {
    for (int j = 1; j < seats.size(); ++ j) {
      dp[i][j] = min(dp[i][j], mn[i - 1][j - 1] + abs(people[i] - seats[j]));
      mn[i][j] = min(mn[i][j - 1], dp[i][j]);
    }
  }
  for (int i = 0; i < seats.size(); ++ i) {
    ans = min(ans, dp[people.size() - 1][i]);
  }
  cout << ans << endl;
  return 0;
}
