#include <stdio.h>
#include <stdlib.h>

#define bool char
#define true 1
#define false 0

int main()
{
    bool V[20000];
    int i;
    int sum=0;
    int limit=1;
    freopen("ciur.in","rt",stdin);
    freopen("ciur.out","wt",stdout);
    scanf(" %d",&limit);
    for(i=1;i<=limit;i++)
        V[i]=true;
    int j;
        for(i=2;i<limit;i++)
            if(V[i]==true)
            {
                sum++;
                for(j=i+i;j<=limit;j+=i)
                    V[j]=false;
            }
    printf("%d",sum);

    return 0;
}