#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main(){
    double b1,b2,b3;cin>>b1>>b2>>b3;
    if(b3*b3+b2*b2-b3*b2-b3*b1==0){
        cout<<0<<endl;
    }
    else{
        cout<<(b3*b3+b2*b2-b3*b2-b3*b1)/(b2-b1)<<endl;
    }   
}