#include <fstream>

using namespace std;
int v[100];
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{int n,i,j,cnt=0;
in>>n;
for(i=2;i<=n;i++)
{if(v[i]==0)
{cnt++;

for(j=i*2;j<=n;j+=i)
v[j]=1;


}
}
out<<cnt;

    return 0;
}