#include <stdio.h>

int fib(int n)
{
    int a=1;
    int b=1;
    int c=0;
    while(n>2)
    {
        c=a+b;
        a=b;
        b=c;
        n--;
    }
    return c;
}



int main() {
    int n =  0;
    int ret = 0;
    scanf("%d",&n);
    ret = fib(n);
    printf("%d",ret);
	return 0;
}