#include<fstream>
#include<iostream>
using namespace std;

char prim[2000000];
int main()
{

long long i,j,n,nrprim=0;
ifstream f("ciur.in");
ofstream g("ciur.out");
    f>>n;
    if(n>2)
        nrprim=1;
	for(i=3;i<=n;i+=2)
		if(prim[i]==0)
		{
			nrprim++;
			for(j=i+i;j<=n;j=j+i)
				prim[j]=1;
		}

    g<<nrprim<<"\n";
    return 0;
}