import std.array, std.stdio, std.conv, std.string, std.math, std.random, std.range,std.functional;
import std.algorithm.searching, std.algorithm.sorting, std.algorithm.iteration, std.algorithm.comparison;
 
long count;
 
void main()
{
    real[] memo;
    real func(long n)
    {
        if(memo[n] != -1)
        {
            return memo[n];
        }
        memo[n] = func(n-1) + func(n-2);
        return memo[n];
    }
    long N = readln().strip.to!long;
    memo.length = N+1;
    memo[] = -1;
    memo[0] = 1;
    memo[1] = 1;
    writeln(func(N));
}
 
