#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
#include<map>
#include<stack>
#include<queue>
#include<list>
using namespace std;
int inf = 1000000000;

int main(void) {

  int b1, b2, b3;
  cin >> b1 >> b2 >> b3;
  cout << (b3*b3 - b3*b1 - b2*b3 + b2*b2) / (b2 - b1) << endl;

  return 0;
}

// EOF