#include <bits/stdc++.h>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int n,cnt;
bool v[2000001];
int main()
{
    int i,j;
    in>>n;
    for (i=2;i<=n;i++)
        v[i]=1;
    for(i=2;i<=n;i++)
        if(v[i])
    {
        cnt++;
        for(j=2*i;j<=n;j+=i)
            v[j]=0;
    }
    out<<cnt;

    return 0;

}