#line 2 "/home/defineprogram/Desktop/Library/template/template.cpp"
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define rep(i, n) for (int i = 0; i < n; i++)
#define REP(i, n) for (int i = 1; i < n; i++)
#define rev(i, n) for (int i = n - 1; i >= 0; i--)
#define REV(i, n) for (int i = n - 1; i > 0; i--)
#define all(v) v.begin(), v.end()
#define PL pair<ll, ll>
#define PI pair<int,int>
#define len(s) (int)s.size()

template <class T, class U>
inline bool chmin(T &a, U b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template <class T, class U>
inline bool chmax(T &a, U b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
constexpr ll inf = 3e18;
#line 2 "main.cpp"


int main() {
    cin.tie(0); ios::sync_with_stdio(false);
    int N;cin>>N;
    double ans=0;
    REP(i,N)ans+=(double)N/i;
    printf("%.12lf\n",ans);
}

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main() {
    std::ios_base::sync_with_stdio(false);

    int N; cin>>N;

    long long sum = 0;

    while(N--){

        long long A; long long B;
        cin>>A>>B;

        sum += (B - A + 1)*(B+A)/2;

    }

    cout<<sum<<"\n";

    return 0;
}
