90pts:

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N=1001;
int m,n;
int a[N]={0},b[N]={0},c[N]={0},x=1000;
void f(int a[],int b[]){
	for(int i=1;i<=1000;i++) a[i]+=b[i];
	for(int i=1;i<=1000;i++){
		if(a[i]>=10){
			a[i+1]+=a[i]/10;
			a[i]%=10;
		}
	}
}
void swapx(int a[],int b[]){
	for(int i=1;i<=1000;i++) a[i]=b[i];
}
signed main(){
	cin>>n;
	a[1]=1;
	b[1]=2;
	if(n<=3){
		cout<<n;
		exit(0);
	}
	for(int i=3;i<=n/*-m-2*/;i++){
		f(a,b);
		swapx(c,a);
		swapx(a,b);
		swapx(b,c); 
	}
	for(int i=1000;i>=1;i--){
		if(c[i]==0) x--;
		else break;
	}
	for(int i=x;i>=1;i--) cout<<c[i];
	return 0;
}