#include<stdio.h>
#include<string.h>

#define input "ciur.in"
#define output "ciur.out"

#define dim 2000001

int n, cont=0;
char a[dim];

int main()
{
	FILE *in, *out;

	in = fopen (input, "r");
	out = fopen (output, "w");

	int i, j;

	fscanf(in, "%d", &n);

    memset(a,1,n+1);

	for(i=2; i<=n; i++)
    
        if(a[i])
        {
              cont++;
        
              for(j=i+i; j<=n; j+=i)
        
			       a[j] = 0;
        }
    
	fprintf(out, "%d\n", cont);

	return 0;

}