#include <cstdio>

#define FOR(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define REV(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define INC(i, n) FOR(i, 0, n)
#define DEC(i, n) REV(i, 0, n)
#define INC1(i, n) FOR(i, 1, (n) + 1)
#define DEC1(i, n) REV(i, 1, (n) + 1)

typedef long long   signed int LL;
typedef long long unsigned int LU;


int n;
LL dp[51];

int main() {
	scanf("%d", &n);
	dp[0] = dp[1] = 1;
	FOR(i, 2, n + 1) { dp[i] = dp[i - 1] + dp[i - 2]; }
	
	printf("%lld\n", dp[n]);
	
	return 0;
}