#include<stdio.h>
unsigned long n,j,i,q=1; bool a[2000000];
int main()
{
    FILE*f=fopen("ciur.in", "r");
    fscanf(f,"%lu",&n); 
    FILE*g=fopen("ciur.out","w");
	if(n%2==0) n--;
    for(i=3;i<=n;i+=2)
        if(a[i]==0)
        {
            for(j=3;j<=n;j+=2) a[j*i]=1;
            q++;
        }
    fprintf(g,"%lu",q);
	fclose(f);
    fclose(g);
    return 0;
}