#include <iostream>
using namespace std;
int fib(int n)
{
if(n<1)
return 0;
if(n==1||n==2)
return 1;
return fib(n-1)+fib(n-2);
}
int fib_loop(int n){
if(n<1)
return 0;
int first=1;
int second=1;
int ret=first;
while(n>2)
{
ret=first+second;
first=second;
second=ret;
--n;
}
return ret;
}
int fib_optimized(int n,int first,int second)
{
if(n<1)
return 0;
if(n==1)
return first;
else if(n==2)
return second;
else
return fib_optimized(n-1,second,first+second);
}
int main() {
int n;
cin>>n;
cout << fib(n)<<endl;
return 0;
}