#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<cstdio>
#include<cstring>
using namespace std;

#define rep(i,n) for(int i=0;i<n;i++)
#define REP(n) rep(i,n)
#define all(n)
const int MAXN = 1000000;

int p[MAXN];

int main()
{
    p[0] = p[1] = 1;
    REP(MAXN)if(!p[i])for(int j=i*2;j<MAXN;j+=i)p[j]=1;

    int n, ans;
    while(cin >> n)
    {
        ans = 0;
        REP(n + 1) ans += !p[i];
        cout << ans << endl;
    }

    return 0;
}