#include <stdio.h>

int main(){
        long x, i, j;
        scanf ("%i", &x);
        if (x<0) x = -x;
        short array_all_numbers[x+1];
        for (i = 0; i<x+1; i++){
                array_all_numbers[i] = 0;
        }
        for (i = 2; i < x+1; i++) {
                if (array_all_numbers[i] == 0) {
                        for (j = i * i; j < x+1; j+=i) {
                                array_all_numbers[j] = 1;
                        }
                }
        }
        for (i = x; i > 1; i--){
                if ((array_all_numbers[i]==0) && ((x%i) == 0)){
                printf("%ld", i);
                break;
                }
        }
	return 0;
}


valgrind показывает ошибки:
==1717== Memcheck, a memory error detector
==1717== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==1717== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==1717== Command: /home/solution
==1717== Parent PID: 1716
==1717==
==1717== Conditional jump or move depends on uninitialised value(s)
==1717== at 0x40068C: main (primediv.c:7)
==1717==
==1717== Warning: client switching stacks? SP change: 0x7ff000170 --> 0xfffffff9ff000150
==1717== to suppress, use: --max-stackframe=60129542176 or greater
==1717== Conditional jump or move depends on uninitialised value(s)
==1717== at 0x400722: main (primediv.c:9)
==1717==
==1717== Use of uninitialised value of size 8
==1717== at 0x40070B: main (primediv.c:10)
==1717==
==1717== Invalid write of size 2
==1717== at 0x40070B: main (primediv.c:10)
==1717== Address 0xfffffff9ff000150 is not stack'd, malloc'd or (recently) free'd
==1717==
==1717==
==1717== Process terminating with default action of signal 11 (SIGSEGV)
==1717== Access not within mapped region at address 0xFFFFFFF9FF000150
==1717== at 0x40070B: main (primediv.c:10)
==1717== If you believe this happened as a result of a stack
==1717== overflow in your program's main thread (unlikely but
==1717== possible), you can try to increase the size of the
==1717== main thread stack using the --main-stacksize= flag.
==1717== The main thread stack size used in this run was 8388608.
==1717== Use of uninitialised value of size 8
==1717== at 0x4A246E0: _vgnU_freeres (in /usr/lib64/valgrind/vgpreload_core-amd64-linux.so)
==1717==
==1717== Invalid write of size 8
==1717== at 0x4A246E0: _vgnU_freeres (in /usr/lib64/valgrind/vgpreload_core-amd64-linux.so)
==1717== Address 0xfffffff9ff000148 is not stack'd, malloc'd or (recently) free'd
==1717==
==1717==
==1717== Process terminating with default action of signal 11 (SIGSEGV)
==1717== Access not within mapped region at address 0xFFFFFFF9FF000148
==1717== at 0x4A246E0: _vgnU_freeres (in /usr/lib64/valgrind/vgpreload_core-amd64-linux.so)
==1717== If you believe this happened as a result of a stack
==1717== overflow in your program's main thread (unlikely but
==1717== possible), you can try to increase the size of the
==1717== main thread stack using the --main-stacksize= flag.
==1717== The main thread stack size used in this run was 8388608.
==1717==
==1717== HEAP SUMMARY:
==1717== in use at exit: 0 bytes in 0 blocks
==1717== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==1717==
==1717== All heap blocks were freed -- no leaks are possible
==1717==
==1717== For counts of detected and suppressed errors, rerun with: -v
==1717== Use --track-origins=yes to see where uninitialised values come from
==1717== ERROR SUMMARY: 6 errors from 6 contexts (suppressed: 2 from 2)

Данные для теста N1:
входные данные

о