#include <bits/stdc++.h>

using namespace std;
char ar[2000005];
int main()
{
    //ios_base::sync_with_stdio(0);cin.tie(0);
    int N;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&N);
	int i, j;
	int p{0};
	for (i=2;i<=N;i++)
        ar[i] =1;
	for (i = 2; i <= N / 2; i++)
	{	if (ar[i])
    {   p++;
		for (j = i+i; j <= N; j+=i)
			ar[j] = 0;
	}
			}
//for (i = 1; i <= N; i++)
	//	if (ar[i]) p++;
    printf("%d\n",p);
	return 0;
}