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

using namespace std;
FILE *f,*g;

char p[2000001];
int main()
{
    int i,j,n,nr=1;
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    for(i=3; i<=n; i=i+2 )
    {
        if(p[i]==0)
        {
            nr++;
        for(j=i; j<=n; j=j+i*2) p[j]=1;
        }
    }
    fprintf(g,"%d",nr);
    fclose(f);
    fclose(g);
    return 0;
}