//Include
#include <stdio.h>

//Variabile
FILE *in, *out;

int n, solutii;

bool neprime[2000001];

//Main
int main()
{
	in=fopen("ciur.in","rt");
	out=fopen("ciur.out","wt");
	fscanf(in, "%d",&n);
	
	for(int i=2;i<=n;++i)
	{
		if(neprime[i])
			continue;
		++solutii;
		for(int j=i;j<=n;j+=i)
			neprime[j]=true;
	}
	
	fprintf(out, "%d",solutii);
	
	fclose(in);
	fclose(out);
	return 0;
}