#include<algorithm>

#include<cmath>

#include<cstdio>

#include<iostream>

using namespace std;

int main(){

int k,a=1,b=1,c=1;

cin>>k;

for(int i=1;i<=k;i++){

//i=1 c=1

//i=2 c=2

//i=3

if(i>=3){

c=a+b;//i=3 a=1 b=1

a=b;//i=4

b=c;//i=4

}

}

cout<<c;

return 0;

}