#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, cnt;
bool v[2000005];

int main()
{
    fin>>n;
    v[0]=v[1]=1;
    for (int i=4, i<=n; i=i+2)
    {
        v[i]=1;
    }
    for (int i=3; i*i<=n; i=i+2)
    {
        if (v[i]==0)
        {
            cnt++;
            for (int j=i*i; j<=n; j=j+(2*i))
            {
                v[j]=1;
            }
        }
    }
    fout<<cnt;
    return 0;
}