#include<stdio.h>
#include<iostream.h>
int N,cnt;
char prim[2000005];
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++)
        prim[i]=1;
    for (i=2;i<=N;i++)
        if (prim[i])
        {
            cnt++;
            for (j=i+i;j<=N;j+=i)
                prim[j]=0;
        }
    printf("%d\n",cnt);
    return 0;
}