#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (n); i++)

using namespace std;

int main() {
    double t0, s, d;
    cin >> t0 >> s >> d;
    double t1 = t0 + d / s;

    double ans = 0;
    rep (i, 1000) {
        ans += max(min<double>(t1, 30 + 24 * i) - max<double>(t0, 18 + 24 * i), 0.0);
    }
    cout << setprecision(10) << ans << endl;

    return 0;
}