#include <bits/stdc++.h> using namespace std; long long n, m, t, ans, x; long long gcd(long long a, long long b) { if (!b) return a; return gcd(b, a % b); } int main() { cin >> n >> m >> t; if (!m) { cout << -1 << endl; exit(0); } if (!n) { cout << 0 << endl; exit(0); } x = gcd(n, m); n /= x; m /= x; while (n != 1 || m != 1) { if (n < m) swap(n, m); ans += n / m; n %= m; if (!n) { n += m; ans--; } if (n < 1 || m < 1) { cout << -1 << endl; exit(0); } } cout << ++ans * t << endl; return 0; }