const memoize = function(proc){
    const cache = {};

    const helper = (n) => {
        if(!cache[n]){
            cache[n] = proc(n);
        }
        return cache[n];
    }

    return helper;
}

const fib = memoize((n) => {
    if(n < 2){
        return 1;
    }
    return fib(n - 1) + fib(n - 2);
});

let input = require('fs').readFileSync('/dev/stdin', 'utf8').split("\n");
console.log(fib(Number(input[0])));
