import java.io.IOException; import java.io.InputStream; import java.util.NoSuchElementException; public class Main { private static FastScanner sc = new FastScanner(); public static void main(String[] args) { double b1 = sc.nextDouble(); double b2 = sc.nextDouble(); double b3 = sc.nextDouble(); if(b2 == b1) { System.out.println(Math.round(b3)); return; } double r = (b3 - b2) / (b2 - b1); System.out.println(Math.round(r * b3 + b2 - r * b1)); } static class FastScanner { private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if(ptr < buflen) { return true; } else { ptr = 0; try { buflen = in.read(buffer); } catch(IOException e) { e.printStackTrace(); } if(buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;} private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;} private void skipUnprintable() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++;} public boolean hasNext() { skipUnprintable(); return hasNextByte();} public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while(isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { return Long.parseLong(next()); } public int nextInt(){ return Integer.parseInt(next()); } public double nextDouble(){ return Double.parseDouble(next()); } } }