#include <bits/stdc++.h>
#define H 2000001
int n, nr;
char ciur[H];
void act(int i){
++nr;
for (int j = i+i; j <= n; j += i)
ciur[j] = 0;
}
int main(void)
{
int i, j;
freopen("ciur.in", "r", stdin); freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
for (i = 2; i <= n; ++i)
ciur[i] = 1;
for (i = 2; i <= n; ++i)
if (ciur[i])
{
act(i);
}
printf("%d\n", nr);
return 0;
}