Ошибка: Утечки памяти Как исправить?

$ cat main.c
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>
int main(){
  unsigned int val; //меняем на беззнаковое
  scanf("%u", &val);
  
  char *prime = malloc((val+1) * sizeof(char));
  if(prime == NULL){ //не забываем проверки!
    fprintf(stderr, "Can not allocate memory\n");
  }
  memset(prime,1,sizeof(char)*(val+1)); //исправлено
  
  prime[0] = prime[1] = 0;
  for (unsigned int i = 2; i <= val; ++i){ //если val ==MAX_UNSIGNED, цикл станет бесконечным
    if (prime[i]){
      for (unsigned int j = i * i; j <= val; j += i){ //тут возможно переполнение при умножении i*i
        prime[j] = 0;
      }
    }
  }
  
  for (unsigned int i = val; i > 0; --i){ //какой смысл проверять на 0?
    if (prime[i]){
      if (!(val%i)){
        printf("%u", i);
        free(prime); //исправлено
        return 0;
      }
      
    }
  }
  
  free(prime);
}
$ gcc main.c -Wall -Wextra
$ valgrind ./a.out 
==7021== Memcheck, a memory error detector
==7021== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==7021== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==7021== Command: ./a.out
==7021== 
123
41==7021== 
==7021== HEAP SUMMARY:
==7021==     in use at exit: 0 bytes in 0 blocks
==7021==   total heap usage: 3 allocs, 3 frees, 2,172 bytes allocated
==7021== 
==7021== All heap blocks were freed -- no leaks are possible
==7021== 
==7021== For counts of detected and suppressed errors, rerun with: -v
==7021== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)