#include<fstream.h>

char ok[2000005];
int i,j,n,k;
long n;
int main()
{	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	fin>>n;
        for(i=2;i*i<=n;i++)
		if(!ok[i])
		{       j=2;
			while(i*j<=n)
			{	ok[i*j]='1';
				j++;
			}
		}
	for(i=2;i<=n;i++)
		if(!ok[i]) k++;
	fout<<k;
        return 0;
}