#include <iostream>
#include <fstream>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
int i,j,n,prim[100],cnt;
int main()
{
    in>>n;
    for(i=2;i<=n;i++)prim[i]=1;
    for(i=1;i<=n;i++)
    {
        if(prim[i]){
            ++cnt;
            for(j=i+i;j<=n;j+=i)
                prim[j]=0;
        }
    }
    out<<cnt;
    return 0;
}