//#include <iostream>
#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

long long n,i,j,db,x[2000001];
int main()
{
    cin>>n;
    x[1]=1;
    i=2;
    while(i<=n)
    {
        if(x[i]==0)
        {
            j=i+i;
            while(j<=n)
            {
                x[j]=1;
                j+=i;
            }
        }
        i++;
    }
   for(i=1;i<=n;++i)
        if(x[i]==0) db++;

        cout<<db;
    return 0;
}