#include<bits/stdc++.h>
using namespace std;
long long n;

long long solve[31];
void init()
{
    solve[0]=0;
    solve[1]=1;
    for(int i=2; i<31; ++i)
    {
        solve[i]=solve[i-1]+solve[i-2];
    }
}


int main()
{
    init();
    while( ~scanf("%lld",&n) )
    {
        printf("%lld\n",solve[n]);
    }

    return 0;
 }