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#include <stdlib.h>
#include <stdio.h>
#include <math.h>
int main()
{
long i, j;
char prime[44712] = {0, 0, [2 ... 44711] = 1};
for (i = 2; i < 212; i++)
if (prime[i])
for (j = i * i; j < 44712; j += i)
prime[j] = 0;
long primes[4648];
j = 0;
for (i = 0; i < 44712; i++)
if (prime[i])
primes[j++] = i;
long l, r;
scanf("%ld %ld", &l, &r);
long imax = (long) sqrt(r);
for (i = 0; i < 4648; i++)
if (primes[i] > imax) {
imax = i;
break;
}
r -= l - 1;
long *list = malloc(r * 4);
for (i = 0; i < r; i++)
list[i] = 1;
long prime0, l0;
for (i = 0; i < imax; i++) {
prime0 = primes[i];
l0 = (l % prime0) ? (prime0 - (l % prime0)) : 0;
l0 = (l + l0 > prime0 * prime0) ? l0 : (prime0 * prime0 - l);
for (j = l0; j < r; j += prime0)
list[j] = 0;
}
long val = 0;
for (i = 0; i < r; i++)
if (list[i])
val++;
printf("%ld\n", val);
return 0;
}
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