#include<iostream>
#include<cstdio>
#include<queue>
#include<vector>
#include<bitset>
#define INF 0x3f3f3f3f
#define mp make_pair
#define pb push_back
#define maxn 2000010
using namespace std;
bitset < maxn > sel;
int n,i,j,nr;

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2; i<=n; ++i)
        if(!sel[i])
        {
            nr++;
            for(j=i; j<=n; j+=i)
                sel[j]=1;
        }
    printf("%d\n",nr);
    return 0;
}