#include<stdio.h>
char v[200000001];
long b,i,j,p;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&b);
    v[1]=1;
    for(i=1;i<=b;i++)
	                 if(v[i]==0)
		                        for(j=2;j*i<=b;j++)
		                                           v[i*j]=1;
    p=0;
    for(i=2;i<=b;i++) if(v[i]==0) p++;
    printf("%ld",p);
    return 0;  
}