#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool s[2000001];
int main()
{
int i,j,nr=0,n;
in>>n;
for(i=2;i<=n;i++)
    {s[i]=1;}
for(i=2;i<=n;i++)
        if(s[i])
            {nr++;
                for(j=i*i;j<=n;j+=i)
                    s[j]=0;
            }
    }
out<<nr;
    return 0;
}