#include<stdio.h>

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

#define dim 2000000

long long unsigned n, cont=1;
char a[dim];

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

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

	long long unsigned i, j;

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

    memset(a,0,n+1);

	for(i=2; i<=n; i++)
    
        if(a[i]=='0')
        {
              cont++;
        
              for(j=i+i; j<=n; j+=i)
        
			       a[j] = '1';
        }
    
	fprintf(out, "%lld", cont);

	return 0;

}