include<fstream.h>
long n,i,j,nr;  
char prim[2000005];  
ifstream f("ciur.in");  
ofstream g("ciur.out");
int main()  
{    
f>>n;  
for(i=2;i<=n;i++)  
prim[i]=1;  
for(i=2;i<=n;i++)  
if(prim[i])  
{  
nr++;
for(j=i+i;j<=n;j=j+i)  
prim[j]=0;  
}  
g<<nr;
f.close();
g.close();  
return 0;  
}