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

using namespace std;

int N, cnt;
char prim[2000005];

int main()
{
    FILE *f =fopen("ciur.in","r");
    FILE *f2=fopen("ciur.out","w");
    fscanf(f,"%d",&N);
    int i;
    for (i=0;i<=N;i++)
    prim[i]=1;
    for (i=2;i<=N;i++)
    {
        if(prim[i]!=0)
            {
             cnt++;
                int j;
                for(j=2*i ;j<=N ;j+=i)
                {
                    prim[j]=0;
                }
            }

    }

    printf(f2,"%d\n",cnt);
    fclose(f);
    fclose(f2);
}