#include <iostream>
#include <stdio.h>
#include <bitset>
using namespace std;
FILE *f,*g;
bitset <2000002> v;
int main()
{
    int n,nr=0,i,j;
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    fscanf(f,"%d",&n);
    for(i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            nr++;
            for(j=i*2;j<=n;j=j+i)
            {
                v[j]=1;
            }

        }
    }

    fprintf(g,"%d",nr);
    fclose(f);
    fclose(g);
    return 0;
}