#include <bits/stdc++.h>
using namespace std;
const long long int MOD = 1000000007;
const long double PI = 2 * acos(0.0);
const vector<long long int> dx = {1, -1, 0, 0};
const vector<long long int> dy = {0, 0, 1, -1};
vector<long long int> ga(long long int n, bool oneIndexed = false) {
  vector<long long int> a;
  if (oneIndexed) a.push_back(0ll);
  for (long long int i = 0; i < n; i++) {
    long long int p;
    cin >> p;
    a.push_back(p);
  }
  return move(a);
}
vector<string> gas(unsigned long long int n, bool oneIndexed = false) {
  vector<string> a;
  if (oneIndexed) a.push_back("");
  for (unsigned long long int i = 0; i < n; i++) {
    string p;
    cin >> p;
    a.push_back(p);
  }
  return move(a);
}
template <typename T, typename A>
void pa(vector<T, A> const &a, long long int begin = 0,
        long long int end = -1) {
  if (end == -1) end = (long long int)a.size() - 1;
  for (long long int i = begin; i <= end; i++) {
    cout << a[i] << " ";
  }
  cout << "\n";
}
template <typename T, typename A>
void papair(vector<T, A> const &a, long long int begin = 0,
            long long int end = -1) {
  if (end == -1) end = (long long int)a.size() - 1;
  for (long long int i = begin; i <= end; i++) {
    cout << a[i].first << " " << a[i].second << "\n";
  }
}
void solve() {
  long long int x, y, m;
  cin >> x >> y >> m;
  if (x > y) {
    long long int c = x;
    x = y;
    y = c;
  }
  if (x + y <= min(x, y) && y < m) {
    cout << -1;
    return;
  }
  long long int steps = 0;
  while (y < m) {
    long long int k = (y - x) / y;
    if (k == 0) {
      steps++;
      x += y;
    } else {
      steps += k;
      x += k * y;
    }
    if (x > y) {
      long long int c = x;
      x = y;
      y = c;
    }
  }
  cout << steps;
}
int main(void) {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
