#include <bits/stdc++.h>

using namespace std;

#define all(X) (X).begin(), (X).end()
#define pb push_back
#define rall(X) (X).rbegin(), (X).rend()
#define ll long long
#define ull unsigned long long
#define ld long double
#define fir first
#define sec second

int main() {
	ll a, b, k; cin >> a >> b >> k;
	ll i = a * 10;
	map<ll, ll> mp;
	ll col = 0;

	while (mp[i] == 0) {
		col++;
		mp[i]++;
		ll q = i / b;
		i = (i % b) * 10;
		if (q == k) {
			cout << col;
			return 0;
		}
	}
	cout << -1;
	return 0;
}