#include <bits/stdc++.h>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool prim[20000001];
int n, cnt=0;
int main()
{ int  i, j;
prim[0]=prim[1]=1;
in>>n;
for(i=2; i*i<=n; i++)

	prim[i]=1;
	for(i=2; i*i<=n; i++)
		if(prim[i]==1)
	{
		for(j=2; j<=n; j=j+i)
	prim[i*j]=1;
	}
	for(i=1;i<=n;++i)
if(prim[i]==0)
cnt++;
out<<cnt;
    return 0;
}