#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,i,j,cnt;
char prim[1000000];
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        prim[i]='1';
    for(i=2;i*i<=n;i=i+1)
        if(prim[i]!='0')
        {
            for (j=i*i;j<=n;j=j+i)
                prim[j]='0';
        }
                for(i=2;i<=n;i++)
                if(prim[i]=='1') 
               cnt++;         
             fout<<cnt;            
    //system("PAUSE");
    return 0;
}