#include <stdio.h>
#include <stdlib.h>
#include <err.h>

int
main(void)
{
        char line[1024];
        size_t i = 0;
        while (fgets(line, sizeof(line), stdin) != NULL) {
                if ((size_t)atoi(line) != i)
                        errx(EXIT_FAILURE, "bad line \"%s\", expected %zu\n",
                            line, i);
                i++;
        }
        return EXIT_SUCCESS;
}