#include <cstdio>
using namespace std;

int main()
{

    long long n;
    int num = 0;
	char prim[2000005];

    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);

	for(long long i = 2; i <= n; ++i)
		prim[i] = 1;
	for(long long i = 2; i <= n; ++i)
		if(prim[i])
		{
			num++;
			for(long long j = i*i; j <= n; j += i)
				prim[j] = 0;
		}

	printf("%d\n", num);

	return 0;
}