import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


/*
  B1 = x
  B2 = r x + d
  B3 = r^2 x + r d + d
  
  B2 = B1 r + d
  B3 = B1 r^2 + r (B2 - B1 r) + (B2 - B1 r) = (B2 - B1) r + B2
  
  r = p / q
  d = B2 - B1 p / q
  B4 = B3 p / q + d = (B3 - B1) (p / q) + B2
*/

void main() {
  try {
    for (; ; ) {
      const B1 = readLong();
      const B2 = readLong();
      const B3 = readLong();
      
      const rp = B3 - B2;
      const rq = B2 - B1;
      assert(((B3 - B1) * rp) % rq == 0);
      const ans = (B3 - B1) * rp / rq + B2;
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}