#include <bits/stdc++.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool v[2000006];
int main()
{
    int n, p=0;

    f>>n;
    for (int i=2;i<=n;i+=2)
        v[i]=true;
    v[2]=false;
    for (int i=3;i<=n/3;i+=2)
    {
        if (!v[i])
        for (int j=i+i;j<=n;j+=i)
            v[j]=true;
    }
    for (int i=1;i<=n;i++)
        if (v[i]==0)    p++;
    g<<p-1;
    return 0;
}