#include<fstream.h>
ifstream f("ciur.in"); ofstream g("ciur.out");
long prim[100],i,n,k,j,mk,c;
int main(){
	f>>n;
	for(i=2;i<=n;++i)
		prim[i]=i;
	for(i=2;i<=n;++i)
		if(prim[i]){
			c++;
			for(j=i+1;j<=n;j+=i)
				prim[j]=0;
		}
	g<<c;
f.close();g.close();
return 0;
}