#include<stdio.h>
#include<vector>

using namespace std;

void ciur(long int n,long int &x)
{	vector<bool> v;
	long int i,j;
	for(i=2;i<=n;i++)
		v.push_back(1);
	for(i=2;i<=n;i++)
		if(v[i]==1)	{
			x++;
			for(j=i+i;j<=n;j=j+i)
					v[j]=0;
		}
}

int main()
{	long int N,nr=0;
	FILE *c,*d;
	c=fopen("ciur.in","r");
	d=fopen("ciur.out","w");
	fscanf(c,"%ld",&N);
	ciur(N,nr);
	fprintf(d,"%ld",nr);
	fclose(c);
	fclose(d);
	return 0;
}