#include<cstdio>
#define rep(i,a) for(int i=0;i<(a);++i)

typedef long long ll;

ll fib[51];

int main()
{
	int N;
	scanf( "%d", &N );

	fib[0] = 1; fib[1] = 1;
	rep( i, N-1 )
		fib[i+2] = fib[i] + fib[i+1];

	printf( "%lld\n", fib[N] );

	return 0;
}