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

int N, contor=0;
char prim[2000001];
 
int main(void)
{
    int i, j;
     
    ifstream f("ciur.in");
    ofstream g("ciur.out");
     
    f>>N;
    for (i=2;i<=N;i++)
        prim[i]=1;
    for (i=2;i<=N;i++)
        if(prim[i])
        {
            contor++;
            for (j=i+i;j<=N;j=j+i)
                prim[j]=0;
        }
 
    g<<contor;
 
    return 0;
}