#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll const mod=1000000007;
ll const md=998244353;
ll mypowr(ll a,ll b) {ll res=1;a%=mod; assert(b>=0);
for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll mypow(ll a,ll b) {ll res=1;assert(b>=0);
for(;b;b>>=1){if(b&1)res=res*a;a=a*a;}return res;}
ifstream in("ciur.in");
ofstream out("ciur.out");
#define mp make_pair
#define pb push_back
#define pf push_front
#define fi first
#define se second

bool f[2000005];

int main()
{   cout<<fixed<<setprecision(12);
    cin.tie(0);cout.tie(0);
    ios_base::sync_with_stdio(0);

    ll cnt=0;
    ll n;in>>n;
    for(ll i=2;i<=n;++i){
        if(!f[i]){
            ++cnt;
            for(ll j=i*i;j<=n;j+=i)f[j]=1;
        }
    }
    out<<cnt<<'\n';






    return 0;
}