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 compNum = (diff >= 0) ? parseInt(fArr[0]) : parseInt(fArr[1])
  if (diff >= 20 || diff >= fArr[2]){
    console.log(Math.floor((compNum + parseInt(fArr[2])) / 2) )
  }else if(diff >= 0) {
    console.log(parseInt(fArr[0]) + Math.floor((parseInt(fArr[2]) - fDiff) / 2))
  }else {
    console.log(parseInt(fArr[1]) + Math.floor((parseInt(fArr[2]) - fDiff) / 2))
  }

});