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

using ll = long long;
using ull = unsigned long long;
using ld = long double;

#define MOD 1000000007LL

#define rep(i, n) for(ll (i) = 0LL;(i) < (ll)(n);(i)++)
#define rep2(i, s, e) for(ll (i) = (ll)(s);(i) < (ll)(e);(i)++)
#define repi(i, n) for(ll (i) = 0LL;(i) <= (ll)(n);(i)++)
#define repi2(i, s, e) for(ll (i) = (ll)(s);(i) <= (ll)(e);(i)++)
#define per(i, n) for(ll (i) = (ll)(n) - 1LL;(i) >= 0LL;(i)--)
#define per2(i, s, e) for(ll (i) = (ll)(s) - 1LL;(i) >= (ll)(e);(i)--)
#define peri(i, n) for(ll (i) = (ll)(n);(i) >= 0LL;(i)--)
#define peri2(i, s, e) for(ll (i) = (ll)(s);(i) >= (ll)(e);(i)--)
#define iter(i, it) for(auto &(i): (it))

template<typename T, typename U> ostream& operator<<(ostream &s, const pair<T, U> m) {
    cout << "(" << m.first << ", " << m.second << ")";
    return s;
}
template<typename T, typename U> ostream& operator<<(ostream &s, const map<T, U> m) {
    ll c = 0;
    cout << "{ ";
    iter(i, m) cout << i << (c++ == m.size() - 1 ? " " : ", ");
    cout << "}";
    return s;
}
template<typename T> ostream& operator<<(ostream &s, const vector<T> &v) {
    cout << "{ ";
    rep(i, v.size()) cout << v[i] << (i == v.size() - 1 ? " " : ", ");
    cout << "}";
    return s;
}
template<typename T> ostream& operator<<(ostream &s, const list<T> &v) {
    ll c = 0;
    cout << "{ ";
    iter(i, v) cout << i << (c++ == v.size() - 1 ? " " : ", ");
    cout << "}";
    return s;
}

int main(void) {
    ll A, B, C, D;
    cin >> A >> B >> C >> D;
    cout << min(A, B) + min(C, D) << endl;
    return 0;
}

#include <bits/stdc++.h>
#define repr(i,from,to) for(int (i)=(from);(i)<(to);(i)++)
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
// const bool debug=true;
const bool debug=false;
#define DEBUG if(debug==true)
#define all(x) begin((x)), end((x))
#define vprint(x) for(auto a:(x)) cout << x << endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const ll MOD = 1000000007;
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) { a = b; return true;}
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) { a = b; return true;}
    return false;
}
int main(void) {
    cin.tie(0);
    ios::sync_with_stdio(false);
    long double n,m,d;
    cin>>n>>m>>d;
    long double ans = (n-d) * 2 * (m-1) / (n*n);
    if (d==0) {
        ans = (m-1) / n;
    }
    printf("%.10Lf\n", ans);
    return 0;
}
