const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void async function () {
    // Write your code here
   const n = parseInt(await readline());
   let arr = new Array(n);
   arr[0] = 1;
   arr[1] = 1;
   for(let i = 2; i < n; i++){
        arr[i] = arr[i-1] + arr[i -2];
    }
   console.log(arr[n-1])
}()