Thread: #intermediate codes

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void f(char *a, char *b, int c) {
    if (a < b && c>0) f(a++, b--, c - 1);
    *a = *a < *b ? *a : ++*b;
}
void main(int argc, char *argv[]) {
    int c = atoi(argv[argc - 1]);
    char *p = argv[atoi(argv[3]) + 1],
        *q = p + strlen(p) - 1;
    f(p, q, c);
    printf("%s", p);
}

Why the output is "bllisemilb" ?