The most distant alphabetically (files)

#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>

int main() {
FILE *s1, *s2;
int symbol = 0, max = 0;

s1 = fopen("bit.txt", "r");
s2 = fopen("bit2.txt", "w");

if (!s1)
printf("Error open bit.txt\n");
else
{
do
{
symbol = fgetc(s1);
if (symbol >= 'a' && symbol <= 'z') {
if (max == 0) max = symbol;
if (max < symbol) max = symbol;
}
} while (symbol != EOF);
fprintf(s2, "%c", (char)(max));
}

fclose(s1);
fclose(s2);
return 0;
}