process.stdin.resume();
process.stdin.setEncoding("utf8");

const reader = require("readline").createInterface({
  input: process.stdin,
  output: process.stdout,
});

const lines = [];

reader.on("line", (line) => {
  lines.push(line);
});

reader.on("close", () => {
  let [x1, y1, x2, y2] = lines[0].split(" ").map(Number);
  console.log(
    Math.sqrt(Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2)).toFixed(5)
  );
});

