#include<iostream>
using namespace std;

unsigned long int k;
unsigned long int a = 1;
unsigned long int b = 1;
unsigned long int c;

FILE *f = fopen("kfib.out","w");

void fibonacci(void)
{

     FILE *f = fopen("kfib.in","r");
     
     fscanf(f,"%d",&k);
     
     for(int i=3;i<=k;i++)
     {
        c = a;
        a = a+b;
        b = c;
     }
    
     fclose(f);
}

int main()
{
    fibonacci();
    fprintf(f,"%u",a);
    fclose(f);
    return 0;
}