#include<stdio.h>
#define N 2000001
int main()
{long n,t,j,k;
char a[N];
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%ld",&n);
for(j=2;j<=n;j++)
     a[j]='0';
k=n-1;
j=2;
while(j*j<=n)
     {if(a[j]=='0')
           {for(t=2;t*j<=n;t++)
           if(a[t*j]=='0')
                  {a[t*j]='1';
                  k--;}}
     j++;} 
printf("%ld",k);
return 0;}