#include<fstream>
#include<iostream>
#include<queue>
using  namespace std;
int main()
{
	freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n;
	scanf("%d",&n);
	char prim[2000001];
	memset(prim,1,sizeof(prim));
	int rez = 0;
	for(int i=2; i<=n; i++)
        if( prim[i]==1 )
        {
            rez++;
            for(int j=2*i; j<=n; j+=i) prim[j] = 0;
        }
    printf("%d",rez);
	return 0;
}