#include <cstdio>
#define repi(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,a) repi(i,0,a)
#define all(a) (a).begin(), (a).end()

using ll = long long;

int N;
ll F[51];

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

  F[0] = 1;
  F[1] = 1;

  rep( i, N+1 ) if( i-2 >= 0 )
    F[i] = F[i-1]+F[i-2];

  printf( "%lld\n", F[N] );
  
  return 0;
}