#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bool ciur[2000005];
int n,i,j,c=1;
int main()
{
    cin>>n;
    ciur[1]=ciur[0]=1;
    for(i=2;i*i<=n;i++)
        if(!ciur[i])
            for(j=2;j*i<=n;j++)
                ciur[i*j]=1;
    for(i=2;i<=n;i++)
        if(!ciur[i])
            c++;
    if(n==0 || n==1)
        c=0;
    cout<<c;
}