/*
TASK:minjumps
LANG:C++
*/   
#include <iostream>
using namespace std;
int a,b,c,d;
int ost;
int main(){
    int n,m,i=0,j,k,l,br=0,br1=0,br2=0;
    cin>>a>>b>>c;
    d=a+b;
    m=0;k=0;
    while(m==0){i=i+a;
                br++; 
                if(i>10000) {m=1;br=-1;goto yyyy;}
                if(i==c) m=1;
                if(i>c){l=i-c;
                        j=(i-c)%b;
                        if((k==1)&&(ost==j)) {br=-1;goto end1;}
                        if(k==0){k=1;ost=j;}
                        if(j==0){br=br+(l/b);
                                     m=1;
                                    }
                       }
               yyyy:a=a;
                    }
          
end1: m=0;i=0;k=0;
 while(m==0){i=i+b;
                br1++;
 if(i>10000) {m=1;br1=-1;goto yyy;}
                if(i==c) m=1;
                if(i>c){l=i-c;
                        j=(i-c)%a;
                        if((k==1)&&(ost==j)) {br1=-1;goto end2;}
                        if(k==0){k=1;ost=j;}
                        if(j==0){br1=br1+(l/a);
                                     m=1;
                                    }
                       }
               yyy:a=a;}
  end2:
       if((br>br1)&&(br1!=-1)) br=br1;
       if(br==(-1)) br=br1; 
  m=0;i=0;k=0;br1=0;
  while(m==0){i=i+d;
                br1=br1+2;
                if(i>10000) {m=1;br1=-1;goto yy;}
                if(i==c) m=1;
                if(i>c){l=i-c;
                        j=(i-c)%a;
                        if((k==1)&&(ost==j)) {br1=-1;goto end3;}
                        if(k==0){k=1;ost=j;}
                        if(j==0){br1=br1+(l/a);
                                     m=1;
                                    }
                       }
               yy:a=a;}
  end3:
       if((br>br1)&&(br1!=-1)) br=br1;
       if(br==(-1)) br=br1; 
   m=0;i=0;k=0;br1=0;
   while(m==0){i=i+d;
                br1=br1+2;
                 if(i>10000) {m=1;br1=-1;goto yyyyy;}
                if(i==c) m=1;
                if(i>c){l=i-c;
                        j=(i-c)%b;
                        if((k==1)&&(ost==j)) {br1=-1;goto end4;}
                        if(k==0){k=1;ost=j;}
                        if(j==0){br1=br1+(l/b);
                                     m=1;
                                    }
                       }
       yyyyy:a=a;        }
  end4:if((br>br1)&&(br1!=-1)) br=br1;
       if(br==(-1)) br=br1; 
  cout<<br;
  cout<<endl;
  return 0;
}                       
                
