/*
TASK:minjumps
LANG:C++
*/
#include<iostream>
using namespace std;
int main()
{
    int n,a,b,i,j,t,min,l=0;
    cin>>b>>a>>n;
    min=n;
    for(i=0;i<=n;i++)
     for(j=0;j<=n;j++)
      if(i*a-j*b==n&&i*a<=100){t=i+j;if(t<min)min=t;l=1;}
    if(l)cout<<min<<'\n';
    else cout<<"-1\n";
    return 0;
}
