#include <iostream>
#include <fstream>

using namespace std;

long long n, i, j, k;
char v[2000001];

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for( i=2; i*i<=n; i++ )
        if(v[i]!=1)
            for( j = i * i; j <= n; j+=i )
                v[j]=1;
                for( i = 2; i < n; i++ )
                    if( v[i] == 0 )
                    k++;
                g << k;
    f.close();
    g.close();
    return 0;
}