#include <iostream>
#include <bitset>
#include <fstream>
#include <stdio.h>
using namespace std;
FILE*f;
FILE*g;
int n,i,j,nr;
bitset <100000>v;
int main()
{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=2*i;j<=n;j+=i)
        v[j]=1;
}
fprintf(g,"%d",nr);
return 0;
}