import std.algorithm, std.array, std.container, std.range;
import std.string, std.conv, std.math;
import std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!int;

  auto dp = new long[n + 1];
  dp[0] = 1;
  dp[1] = 1;

  for (auto i = 2; i <= n; ++i) {
    dp[i] = dp[i - 2] + dp[i - 1];
  }

  writeln(dp[n]);
}