#include<bits/stdc++.h>
#define int long long
using namespace std;
signed add(char a1[5010],char b1[5010]){
	int a[5010],b[5010],c[5010],lena,lenb,lenc,x;
	memset(a,0,sizeof(a));
	memset(b,0,sizeof(b));
	memset(c,0,sizeof(c));
	lena = sizeof(a1);
	lenb = sizeof(b1);
	for(int i = 0 ; i < lena ; i++) a[lena - i] = a1[i] - 48; 
	for(int i = 0 ; i < lenb ; i++) b[lenb - i] = b1[i] - 48;
	lenc = 1;
	x = 0;
	while(lenc <= lena || lenc <= lenb){
		c[lenc] = a[lenc] + b[lenc] + x;
		x = c[lenc] / 10;
		c[lenc] %= 10;
		lenc++;
	}
	c[lenc] = x;
	if(c[lenc] == 0) lenc--;
	for(int i = lenc ; i > 0 ; i++) cout<<c[i];
}
signed slt(int N){
	cin>>N;
	if(N == 1) cout<<1;
	if(N == 2) cout<<2;
	string s1 = N + " ";
	else add(slt(s1-1),slt(s1-2));
} 
signed main(){
	slt();
	return 0;
}