#include <stdio.h>

using namespace std;

FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");

int N,k,v[2000000];

int ciur()
{
    for(int i=2;i<=N;i++)
     if(v[i]==0)
     {
        for(int j=i+i;j<=N;j+=i)
         v[j]=1;
        k+=1;
     }
     return 0;
}

int main()
{
    fscanf(f,"%d",&N);
    ciur();
    fprintf(g,"%d",k);
    fclose(g);
    return 0;
}