#include <stdio.h>

int main(void)
{
    FILE *f,*g;
    long j,n,i,cont=0;
    short a[2000000];
    
    f=fopen("ciur.in","r");
    g=fopen("ciur.out","w");
    
    fscanf(f,"%ld",&n);
    for(i=1;i<=n;i++) a[i]=1;
    for(i=2;i<=n;i++)
    {
	if(a[i]==1)
	{
	    cont++;
	    for(j=i+i;j<=n;j+=i) a[j]=0;
	}
    }
    fprintf(g,"%ld",cont);
    
    
    fclose(f);
    fclose(g);
    
    return 0;
}