#include <stdio.h>
bool marcat[2000005] = {false};

void marcheaza(int i, int n)
{
     for (int j = i; j <= n; j += i) {
         marcat[j] = true;
     }
 }

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    
    int n, i, nr = 0;
    scanf("%d", &n);
    
    for (i = 2; i <= n; i++) {
        if (marcat[i] == false) {
           nr++;
           marcheaza(i,n);              
        }
    }
    
    printf("%d",nr);
    
    return 0;
}