#include <iostream>
#include<bitset>
#include<fstream>
using namespace std;
bitset<20000001> ciur;

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int d,n,i,s=0;
    fin>>n;
    for ( d = 2; d * d <= n; d++ )
        if ( ciur[d] == 0 )
            for ( i = d * d; i <= n; i = i + d ) ciur[i] = 1;
    for(i=2;i<=n;i++)if(ciur[i]==0)s++;
    fout<<s;
    return 0;
}