#include <iostream>
#include <fstream>
using namespace std;

int main()
{int i,j,n,terminat=0,a[50],b[50],S=0;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
f>>n;
for (i=0;i<(n-1)/2;i++) a[i]=2*i+3;
b[0]=2;j=0;
while (!terminat)
{for (i=0;i<(n-1)/2;i++)
    if (a[i]%b[j]==0) a[i]=0;
    for (i=0;a[i]==0;i++);
    if (i<(n-1)/2) {b[++j]=a[i]; S=S+1;}
    else terminat=1;
}
g<<S+1;
f.close();
g.close();
    return 0;
}