Help me, please.

README.md

gcc hash.c -o hash -lcrypto -lssl -Wall
./hash

hash.c

#include <stdio.h>
#include <string.h>
#include <openssl/sha.h>

#define MIN_SIZE 16
#define LOW_SIZE 64
#define MID_SIZE 128
#define MAX_SIZE 256

int to_hex(char *src, char *result);

int main(void) {
    char input[MIN_SIZE];               // variable for combined input
    input[0] = '\0';                    // initialize it for strcat later

    char part_one[MIN_SIZE] = "Levi";   // part one of input
    char part_two[MIN_SIZE];            // empty part two of input
    
    int num = 81;                       // int part two
    sprintf(part_two, "%i", num);       // convert int to char

    strcat(input, part_one);            // store part one in input
    strcat(input, part_two);            // store part two in input
    input[strlen(input)] = '\0';        // null terminate string

    printf("%s\n", input);              // show it on the screen

    //--------------------
    
    size_t len = strlen(input);         // length of input
    unsigned char md[LOW_SIZE];         // message digest
    unsigned char message[LOW_SIZE];    // OpenSSL SHA512 requires unsigned char
    
    memcpy(message, input, len);        // copy the input to the unsigned char
    printf("%s\n", message);            // make sure message contains input
    
    SHA512(message, len, md);           // Get the hash and store it in md

    char sha_result[MID_SIZE];          // Need to store the message in a reg char
    memcpy(sha_result, md, LOW_SIZE);   // copy the unsigned md to signed char

    char hash[MID_SIZE];                // Variable to store hex
    to_hex(sha_result, hash);           // convert sha result to hex

    printf("%s\n", hash);               // display it on the screen

    return 1;
}

int to_hex(char *src, char *result) {
    int digit;
    char *src_p, *buffer_p, *buffer_end_p;
    char buffer[MAX_SIZE];

    buffer_p = buffer;
    buffer_end_p = &buffer[MAX_SIZE - 2];
    src_p = src;
    int i;
    for(i=0; i<SHA512_DIGEST_LENGTH; i++) {
        digit = (*src_p >> 4) & 0xf;
        *buffer_p++ = ( digit > 9 ) ? digit + 'a' - 10 : digit + '0';

        digit = *src_p & 0xf;
        *buffer_p++ = ( digit > 9 ) ? digit + 'a' - 10 : digit + '0';

        // safety net
        if(buffer_p >= buffer_end_p) {
            break;
        }
        src_p++;
    }

    *buffer_p = '\0';

    strcpy(result, buffer);

    return 1;
}