#include <bits/stdc++.h>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool v[2000000];
int main()
{
    long long c=0, n, i, i2;
    in >> n;
    for(i=2;i<=n;i++)
        v[i]=1;
    for(i=2;i<=n;i++)
    if(v[i])
    {
        c++;
        for(i2=2*i;i2<=n;i2+=i)
            v[i2]=0;
    }
    out << c;
    return 0;
}