#include <iostream>

using namespace std;
int v[2000001];
int main()
{
    int n, s=0, x, i;
    cin>>n;
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
            s++;
        x=i;
        while(x<=n)
        {
            v[x]=1;
            x+=i;
        }
    }
    cout<<s;
    return 0;
}