const reader = require("readline").createInterface({
  input: process.stdin, output: process.stdout
});
let lines = [];
reader.on("line", line => { lines.push(line);
});
reader.on("close", () => {
  let moji = lines[0].length
  let ans = lines[0].substr(0, moji / 2)
  let ansBack = lines[0].substr(moji / 2, moji)
  if (ans == ansBack) {
    console.log("YES")
  } else {
    console.log("NO")
  }
});