#include"iostream"

#include"memory.h"

#define MAX 1000000

using namespace std;

int index[MAX];

int main()

{

	memset(index, -1, sizeof(index));

	index[1] = 0;

	int sum = 0;

	for(int i = 2; i < MAX; i++)

	{

		if(index[i] == -1)

		{

			sum++;

			for(int j = i; j < MAX; j+= i)

			index[j]=sum;

		}

	}

	int n;

	while(scanf("%d", &n) != EOF)

		printf("%d\n", index[n]);

    return 0;

}