#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>

int main(int argc, char **argv) {


    int BUFSIZE = 3, n, i, fd;
    char c[BUFSIZE];
    
    if ((argc - 1) % 2 != 0) {
	printf("non pari\n");
	exit(EXIT_FAILURE);
    }
    
    memset(c, 0, BUFSIZE);
    
    for (i = 1; i <= (argc - 1) / 2; i++) {
	fd = open(argv[i], O_RDONLY);
	if (fd < 1) {
	    printf("errore file %s\n", argv[i]);
	    exit(EXIT_FAILURE);
	}
	lseek(fd, (long)(i - 1), SEEK_SET);
	n = read(fd, c, 1);
	if (n <= 0) {
	    printf("errore nella read\n");
	    exit(EXIT_FAILURE);
	}
	close(fd);
	
	fd = open(argv[argc - i], O_RDONLY);
	if (fd < 1) {
	    printf("errore file %s\n", argv[argc - i]);
	    exit(EXIT_FAILURE);
	}
	lseek(fd, (long)-i, SEEK_END);
	n = read(fd, c + 1, 1);
	if (n <= 0) {
	    printf("errore nella read\n");
	    exit(EXIT_FAILURE);
	}
	close(fd);
	
	printf("%s", c);	
    }
    
    printf("\n");
    exit(EXIT_SUCCESS);
}