#include<stdio.h>
//台阶/级  步数/步
//1           1
//2           2
//3           3
//4           5
//5           8
//6           13

int p(int t){
    if (t == 1)
        return 1;
    if (t == 2)
        return 2;
    return p(t - 1) + p(t - 2);


}

int main() {
    int n;
    scanf("%d",&n);
    printf("%d\n", p(n));


    return 0;
}