#include <iostream>
#include <fstream>
using namespace std;
int main()
{
    ifstream fcin("ciur.in");
    ofstream fcout("ciur.out");
    int n,i,j;
    fcin>>n;
    int v[n+1],ap[n+1];

    for(i=2;i<=n;i++)
        ap[i]=0;

    for(i=2;i<=n;i++)
        if(ap[i]==0)
            for (j=i*2;j<=n;j+=i)
                ap[j]=1;

    int s=0;
    for (i=2;i<=n;i++)
        if (ap[i]==0)
            s++;
    fcout<<s;

    return 0;
}