#include using namespace std ; #define pb(n) push_back(n) #define fi first #define se second #define all(r) begin(r),end(r) #define vmax(ary) *max_element(all(ary)) #define vmin(ary) *min_element(all(ary)) #define debug(x) cout<<#x<<": "< name(size,init) #define vvl(v,w,h,init) vector> v(w,vector(h,init)) #define mp(a,b) make_pair(a,b) #define rep(i,n) for(int i = 0; i < (int)(n);++i) #define REP(i,a,b) for(int i = (a);i < (int)(b);++i) #define repi(it,array) for(auto it = array.begin(),end = array.end(); it != end;++it) #define repa(n,array) for(auto &n :(array)) using ll = long long; using pii = pair ; using pll = pair ; template void O(T t){ cout << t << endl; } const ll mod = 1e9+7; constexpr ll inf = ((1<<30)-1)*2+1 ; constexpr double PI = acos(-1.0) ; double eps = 1e-10 ; const int dy[] = {-1,0,1,0,1,-1,1,-1}; const int dx[] = {0,-1,0,1,1,-1,-1,1}; inline bool value(int x,int y,int w,int h){ return (x >= 0 && x < w && y >= 0 && y < h); } int main(){ cin.tie(0); ios::sync_with_stdio(false); double b3,b2,b1; double d,r; cin >> b1 >> b2 >> b3; std::cout << b3 + (b3-b2)*(b3-b2)/(b2-b1) << std::endl; return 0; }