#include <iostream>
using namespace std;
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int n;
    cin >> n;
 
    int pole[300001];
    for (int i = 0; i <= n; i++) {
        cin >> pole[i];
    }
 
    if (pole[0] == 1 || pole[n] == 1) {
        cout << -1 << "\n";
        return 0;
    }
 
    int fib[50];
    fib[0] = 1;
    fib[1] = 2;
    int ilosc = 2;
    while (true) {
        fib[ilosc] = fib[ilosc - 1] + fib[ilosc - 2];
        if (fib[ilosc] > n) break;
        ilosc++;
    }
    int dp[300001];
    for (int i = 0; i <= n; i++) dp[i] = -1;
    dp[0] = 0;
    for (int i = 0; i <= n; i++) {
        if (dp[i] == -1) continue;
        for (int j = 0; j < ilosc; j++) {
            int nastepny = i + fib[j];
            if (nastepny <= n && pole[nastepny] == 0) {
                if (dp[nastepny] == -1 || dp[nastepny] > dp[i] + 1) {
                    dp[nastepny] = dp[i] + 1;
                }
            }
        }
    }
    cout << dp[n] << "\n";
    return 0;
}