///Ciurul lui Eratosthenes
#include <stdio.h>
#include <stdlib.h>
#define MAX 2000000
int n;
char ciur[MAX];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int i, j, nr = 0;
    scanf("%d",&n);
    for ( i = 2; i <= n; i++)
        if( ciur[i] == 0){
            nr++;
            for(j= i*i; j<= n; j +=i)
                ciur[j] = 1;
        }
    printf("%d",nr);
    return 0;
}