#include <iostream>

using namespace std;
int n,i,c,j;
bool v[2000001];

int main()
{
    cin>>n;
    c++;
    for (i=3;i<=n;i=i+2) v[i]=1;
    for (i=3;i<=n;i+=2)
    {
        if (v[i])
        {
            c++;
            for (j=i+i;j<=n;j+=i) v[j]=0;
        }
    }
    cout<<c;
}