#include<bits/stdc++.h>
using namespace std;
int main()
{
    long long a=1,b=1,c=1;
    int n;
    cin>>n;
    for (int i=3;i<=n;i++)
	{
	    c=a+b;
		a=b;
		b=c;	
	}
	cout<<c;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
int a=1,b=1,c=1;
int n;
cin>>n;
for(int i=3;i<=n;i++)
{
	c=a+b;
	a=b;
	b=c;
 } 
 cout<<c;
return 0;
}

#include<bits/stdc++.h> using namespace std; int main(){ int a,b,c,k; a=1,b=1,c=1; cin>>k; for(int i=3;i<=k;i++){ c=a+b; a=b; b=c; } cout<<c;

return 0;

}

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c;
	c=1,b=1,a=1;
	int n;
	cin>>n;
	for(int i=3;i<=n;i++)
	{
		c=a+b;
		a=b;
		b=c;
	}
	cout<<c;
	return 0; 
	
}

#include <bits/stdc++.h>
using namespace std;
int f[50]; 
int fibonacci(int n) {
	if(f[n]!=0) return f[n];
    if (n <= 1){
    	f[1]=1;
        return 1;
    }
    if (n == 2){
    	f[2]=1;
        return 1;
    }
    if (n > 2){
    	f[n]=fibonacci(n - 1) + fibonacci(n - 2);
        return fibonacci(n - 1) + fibonacci(n - 2);
    }
}
int main(){
    int k;
    cin >> k;
    cout << fibonacci(k);

    return 0;
}

https://lizikid.cn/p/A1120/solution/668f40d2744de43309b4196a