#include <bits/stdc++.h>
using namespace std;
using ll = long long;
void solve()
{
int a, b, c;
cin >> a >> b >> c;
vector<bool> check(b, false);
int rem = a % b;
int count = 0;
while (true)
{
rem *= 10;
int digit = rem / b;
count++;
if (digit == c)
{
cout << count << endl;
break;
}
rem = rem % b;
if (check[rem] == true)
{
cout << -1 << endl;
break;
}
else
{
check[rem] = true;
}
}
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(nullptr);
solve();
return 0;
}
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