#include <stdio.h>
 #include <iostream>
int n, contor;
char  a[2000000]; 

int main()
{
int i, j;
 
freopen("ciur.in", "r", stdin);
freopen("ciur.out", "w", stdout);
 
scanf("%d", &n);
if(n>1)
{
for (i = 2; i <= n; ++i)
{a[i] = 1;
}
for (i = 2; i <= n; ++i)
if (a[i])
{
++contor;

for (j = i+i; j <= n; j =j+ i)
a[j] = 0;

}
 
printf("%d\n", contor);
}
return 0;
}