#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n;
bool v[2000005];

//optimizat
int sieve1()
{
    int k=1;
    for(int i=4; i<=n; i+=2)
        v[i]=1;
    v[0]=v[1]=1;
    for(int i=3; i*i<=n; i+=2)
        if(!v[i])
        {
            k++;
            for(int j=i*i; j<=n; j+=i)
                v[j]=1;
        }
    return k;
}

//clasic
int sieve2()
{
    int k=0;
    for(int i=2; i<=n; i++)
        if(!v[i])
        {
            k++;
            for(int j=2*i; j<=n; j+=i)
                v[j]=1;
        }
    return k;
}

//optimizat pe biti
int sieve3()
{
    ///!!v unsigned char
    int k=1, i2;
    for(int i=3; i<=n; i+=2)
    {
        if(v[i>>4] & (1<<((i>>1)&7)))
            continue;
        k++;
        for(int j=i+(i2=2*i); j<=n; j+=i2)
            v[j>>4]|=1<<((j>>1)&7);
    }
    return k;
}

int main()
{
    fin >> n;
    fout << sieve1();
    return 0;
}