#include <stdio.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>

int n = 35;

int fib(int x) {
    if (x < 2) {
      return x;
    }
    return fib(x - 1) + fib(x - 2);
}

int main(int argc, char *argv[]) {
    if (argc > 1) {
        char*p;

        errno = 0;
        long conv = strtol(argv[1], &p, 10);

        // Check for errors: e.g., the string does not represent an integer
        // or the integer is larger than int
        if (errno != 0 || *p != '\0' || conv > INT_MAX || conv < INT_MIN) {
            printf("invalid argument: %s\n", p);
            exit(1);
        }

        n = conv;
    }

    printf("%d\n", fib(n));
}