const reader = require("readline").createInterface({
  input: process.stdin,
  output: process.stdout
});
let lines = [];
reader.on("line", line => {
  lines.push(line);
});
reader.on("close", () => {
  const fArr = lines[0].split(' ')
  const diff = parseInt(fArr[0] - fArr[1])
  const fDiff = (diff >= 0) ? diff : diff * -1
  const ans = (diff >= 0) ? parseInt(fArr[0]) + Math.floor((parseInt(fArr[2]) - fDiff) / 2) : parseInt(fArr[1]) + Math.floor((parseInt(fArr[2]) - fDiff) / 2)
  console.log(ans)
});