#include <bits/stdc++.h>
using namespace std;
long long M;
long long solve(long long A, long long B) {
  if (B >= M) return 0;
  long long S = A + B;
  if (S <= A) return -1;
  long long x = (B + B - A - 1) / B;
  if (A + x * B == B) x++;
  return solve(B, A + x * B) + x;
}
int main() {
  long long A, B;
  cin >> A >> B >> M;
  cout << solve(min(A, B), max(A, B)) << endl;
  return 0;
}
