# include <fstream>
#define N 2000001 
using namespace std;
char c[N]; 
long long n; 
void ciur() 
{ 
int d=2; 
while (d*d<=n) 
{ 
if (!c[d]) 
for (int i=d*d; i<=n; i+=d) 
c[i]=1;++d; 
} 
long long num=0; 
for (int i=2; i<=n; ++i)
if (!c[i]) num++; 
ofstream g("ciur.out");
g<<num;
g.close();
} 
void citire() 
{ 
ifstream f("ciur.in"); 
f>>n; 
f.close();
} 
int main() 
{ 
citire(); 
ciur(); 
return 0; 
}