Sieve of Eratosthenes(mod)

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <math.h>
#include <string.h>
#define EPS 1e-8
#define pi 3.1415926535897932384626433832795028841971693993751
#define N 2147483647

int k, ar[20000010];
int ar2[20000010];

void SieveOfEratosthenes()
{
    int t, i, j, l, n, x;

    for (i = 1; i <= 20000000; i++) ar[i] = i;

    for (x = 2; x <= 4473;)
    {
        for (i = (x * x); i <= 20000000; i = i + x)
        {
            ar[i] = 0;
        }

        for (i = x + 1; ;i++)
        {
            if (ar[i] != 0) {x = i; break;}
        }
    }

    k = 0;
    for (i = 2; i <= 20000000; i++)
    {
        if (ar[i] != 0) {ar2[k] = ar[i]; k++;}
    }
}

int main()
{
    int i, j, n;
    SieveOfEratosthenes();
    for (; ;)
    {
        scanf("%d", &n);
        printf("%d\n", ar2[n - 1]);
    }
}