#include <bits/stdc++.h>

using namespace std;
bitset<2000001> a;

int main()
{
    int i,j,n,cnt;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    a[0]=a[1] = 1;
    for(i=4;i<=n;i+=2)
       a[i]=1;
    for(i=3;i*i<=n;i+=2)
       if (a[i]==0)
            for(j=i*i;j<=n;j+=(2*i))
               a[j]=1;

    cnt=0;
    for(i=2;i<=n;i++)
        if(a[i]==0)cnt++;
    fout<<cnt<<"\n";
    fout.close();

    return 0;
}