
const fs = require("fs");
const filePath = process.platform === "linux" ? "/dev/stdin" : "./예제.txt";
let input = fs.readFileSync(filePath).toString().trim();
// const fs = require('fs');
// let input = fs.readFileSync('/dev/stdin').toString().trim();
let n = +input
let dp = new Array(n + 1).fill(0)
dp[0] = 0
dp[1] = 1
const answer = (N) => {
if (N >= 2) {
for (let i = 2; i <= N; i++) {
dp[i] = BigInt(dp[i - 1]) + BigInt(dp[i - 2])
}
}
console.log(dp[N].toString())
}
answer(n)