#include<cstdio>
#include<math.h>
#include<vector>

using namespace std;
int v[2000000];

int main()
{
	int n,i,nr,j,t;
	FILE *f=fopen("ciur.in","r");
	FILE *g=fopen("ciur.out","w");
	fscanf(f,"%d ",&n);
	nr=n-1;
	t=round(sqrt(n));
	for (i=2;i<=t+1;i++)
	{
		if (v[i]==0)
		{
			j=i;
			nr++;
			while (j<=n)
			{
				if (v[j]==0)
				{
					v[j]=1;
					nr--;
				}
			j=j+i;
			}
		}
	}
	fprintf(g,"%d",nr);
	fclose(f);
	fclose(g);
	return 0;
}