#include <iostream>
#include <stdio.h>

using namespace std;

int i,j,n;
int v[500000];

int main()

{  
     freopen("ciur.in", "rt", stdin);
    freopen("ciur.out", "wt", stdout);
   cin>>n;

    for(i=2;i<=n;i++)
    v[i]=1;

    for(j=2;j<=n;j++)
    if (v[j]==1)
    {
    for (int k=2*j; k<=n; k=k+j)
    v[k]=0;
}

int sol=0;
for (i=2; i<=n; i++)
sol = sol+v[i];

cout<<sol;
        
    return 0;
}