---

#include <stdio.h>

int fibonacci(int n) {
    int result;

    if (n == 0) {
        result = 0;
    } else if (n == 1) {
        result = 1;
    } else {
        result = fibonacci(n - 1) + fibonacci(n - 2);
    }

    return result;
}

int main(void) {
    int n;
    char extra;

    if (scanf("%d%c", &n, &extra) != 2 || extra != '\n' || n < 0) {
        printf("n/a");
    } else {
        printf("%d", fibonacci(n));
    }

    return 0;
}