#include <iostream>
#include <fstream>
using namespace std;
long long n,s;
bool v[2000000];
int main()
{
    ifstream fi("ciur.in");
    fi>>n;
    fi.close();
    for (long i=0;i<n;i++)
        v[i]=1;
    v[0]=0;v[1]=0;
    for (long i=2;i<n;i++)
        if (v[i]==1) {
            s++;
            for (long j=i+i;j<n;j=j+i)
                v[j]=0;
        }
    ofstream fo("ciur.out");
    fo<<s;
    fo.close();
    return 0;
}