#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;

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