#include <stdio.h>

int main(int argc, char **argv)
{
    FILE *fp0, *fp1;
    int x, y;
    int eof0, eof1;  /* EOF if eof (hence we didn't call them "iseof") */

    if (argc != 3) {
        fprintf(stderr, "usage: %s file1 file2\n", argv[0]);
        return 1;
    }

    if ((fp0 = fopen(argv[1], "r")) == NULL) {
        perror(argv[1]);
        return 1;
    }
    if ((fp1 = fopen(argv[2], "r")) == NULL) {
        perror(argv[2]);
        return 1;
    }

    eof0 = fscanf(fp0, "%d", &x);
    eof1 = fscanf(fp1, "%d", &y);
    while (eof0 != EOF && eof1 != EOF) {
        if (x < y) {
            printf("%d\n", x);
            eof0 = fscanf(fp0, "%d", &x);
        } else {
            printf("%d\n", y);
            eof1 = fscanf(fp1, "%d", &y);
        }
    }
    while (eof0 != EOF) {
        printf("%d\n", x);
        eof0 = fscanf(fp0, "%d", &x);
    }
    while (eof1 != EOF) {
        printf("%d\n", y);
        eof1 = fscanf(fp1, "%d", &y);
    }

    return 0;
}