#include<bits/stdc++.h>

using namespace std;

#define S(a) scanf("%d",&a)
typedef long long ll;

int main() {

    {
        int a, b, c;
        S(a), S(b), S(c);
        // check if number a is divisible by  b
        if (a % b == 0) {
          // if required digit is 0 the print 1 because 4/ 2 = 2.0
            if (c == 0) {
                printf("1\n");
            } else

                printf("-1\n");
            return 0;
        }

       // map to check repeated remainder
        unordered_map<int, bool> map;

        // simulate the division process
        int i = 1;
        bool rep =0;
        for (ll r = a % b; r; r %= b) {

            // meet a known remainder
            // so we reach the end of the repeating part
            if (map.find(r) != map.end()) {
   rep = 1;
                break;
            }

            // the remainder is first seen
            // remember it
            map[r] = 1;

            r *= 10;
            //found digit break
            if ((r / b) == c) {
                printf("%d\n", i);
                return 0;
            }
            i++;
        }
        if (!rep &&c == 0) {
            printf("%d\n", i);
        } else
            printf("-1\n");
    }

    return 0;
}