#include <bits/stdc++.h>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

bitset<2000100>a;
int n;

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