#include <iostream>
///ifstream fin("ciur.in");
///ofstream fout("ciur.out");
using namespace std;
int v[1000001];
int main()
{
    v[0]=v[1]=1;
    int n,i,j,cnt=0;
    cin>>n;
    for(i=4;i<=n;i+=2)
    {
        v[i]=1;
    }
    for(i=3;i*i<=n;i+=2)
    {
        if(v[i]==0)
        {
            for(j=i*i;j<=n;j+=i)
                v[j]=1;
        }
    }
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
            cnt++;
    }
cout<<cnt;
    return 0;
}