---

#include <stdio.h>

int fibonacci(int number);

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

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

    printf("%d", fibonacci(number));

    return 0;
}

int fibonacci(int number) {
    int result;

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

    return result;
}