https://www.acmicpc.net/problem/2747
using System;
class Program
{
static void Main() {
string s=Console.ReadLine();
int n=int.Parse(s);
int[] f=new int[n+1];
f[1]=1;
for(int i=2;i<=n;i++){
f[i]=f[i-1]+f[i-2];
}
Console.Write(f[n]);
}
}