/*
TASK: minjumps
LANG: C++
*/
#include <iostream>
using namespace std;
int main()
{
    int n; // kraina cel
    int a, b;
    int jumps = 0;
    int jumped = 0;
    cin >> a >> b >> n;
    if (b > a) swap(a, b);
    // nechetna tochka, chetni skokove
    if (a % 2 == 0 && b % 2 == 0 && n % 2 == 1)
    { cout << -1 << endl; return 0; }
    if (a > b)  // moje li da se dostigne samo sus golemi skokove
    {           // 
          for (int i = 0; jumped < n; ++i) 
          { jumped += a; jumps++; }
          if (jumped == n)
          { cout << jumps << endl; return 0; }
          jumped = 0; jumps = 0;
    }

    do
    {
          jumped += a;

          ++jumps;
          if (jumped > n)
          { 
          do
          { jumped -= b; ++jumps; } while (jumps > n);
          if (jumped == n) { cout << jumps << endl; return 0; }
          }
    } while (jumps != n);
              
   
    return 0;
}