#include <iostream>
using namespace std;
int main(void){
    long long a,b,c;
    cin>>a>>b>>c;
    if(b>=c){
        int f=0;
        if((c)%a==0){
            cout<<(c)/a<<endl;
            f++;
        }        
        if((c+b)%a==0){
            cout<<(c+b)/a<<endl;
            f++;
        }

        if(f==0){
            cout<<-1<<endl;
        }
    }else{
        if((c+b)%a==0){
            cout<<(c+b)/a<<endl;
        }else{
            cout<<-1<<endl;
        }
    }
    return 0;
}