#include<fstream>
using namespace std;
bool v[2000002];
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n, i, j, m, r=0;
    in>>n;
    v[0]=1;
    v[1]=1;
    for(i=2;i*i<=n;i++)
    {
        if(v[i]==0)
        {
            for(j=2*i;j<=n;j=j+i)
            {
                v[j]=1;      //elimin multiplii lui c
            }
        }
    }
    for(i=1;i<=n;i++)
    {
        if(v[i]==0)
            r++;
    }
    out<<r;
    return 0;
}