#include<stdio.h>
#include<math.h>
int main(void)
{
long a=1;
long b=1;
int n;
int k;
printf("input number:");
scanf("%ld",&k);
for(n=0;n<=(k-3);n++)
{
a=a+b;
b=a+b;
}
if(k%2==1)
printf("%ld\n",a);
else if(k%2==0)
printf("%ld\n",b);
else
printf("error");
}