#include<stdio.h>
#include<bitset>
using namespace std;
FILE *in=fopen("ciur.in","rt");
FILE *out=fopen("ciur.out","wt");
bitset<2000001> prim;
int i,n,cont;
int main()
{
	fscanf(in,"%d",&n);

	cont=1;
	for(i=3;i<=n;i+=2)
	{
		if(!prim[i])
		{
			for(long long j=1LL*i*i;j<=n;j+=i)
				prim[j]=true;
			cont++;
		}
	}
	fprintf(out,"%d",cont);
}