#include <stdio.h>

#include <stdlib.h> // Judge i Is it prime , You need to determine i Can be (long)sqrt(i) Divide the number within

// if i Divisible by one of the prime numbers , be i Not prime ; otherwise i Prime number int main()

{

//n=10 ans=4

//n=100 ans=25

//n=1000 ans=168

//n=10000 ans=1229

//n=100000 ans=9592

//n=1000000 ans=78498

//n=10000000 ans=664579

//n=100000000 ans=5761455

long i,j,n,flag,ans=,t=;

long *zhi=(long *) malloc (sizeof(long)*);

scanf("%ld",&n);

zhi[]=;

for (i=;i<=n;i++)

{

// if "zhi[t]*zhi[t]==i" establish , be i Not prime , Don't continue to judge

// And greater than i You need to use zhi[t] Judge (j=0;j<t+1;j++)

// This method is better than " When the prime number is greater than (long)sqrt(i) Exit from time " Fast

// and (zhi[t]-1)*(zhi[t]-1)<=i<=n

// When i Less than longint The scope can be realized

if (zhi[t]*zhi[t]==i)

{

t++;

continue;

}

flag=;

for (j=;j<t;j++)

if (i%zhi[j]==)

{

flag=;

break;

}

if (flag)

{

zhi[ans]=i;

ans++;

}

}

printf("ans=%ld\n",ans);

/*

for (i=0;i<ans;i++)

printf("%ld ",zhi[i]);

printf("\n");

*/

/*

if (zhi[ans]==n)

printf("%ld is a prime\n",n);

else

printf("%ld is not a prime\n",n);

*/

return ;

}

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