#include <bits/stdc++.h>
#define rep(i,l,r) for(int i=(l); i<(r); i++)
#define INF ((1LL<<62)-(1LL<<31)) 
using namespace std;
using ll = long long;
using inv = vector<int>;
using stv = vector<string>;
using GraphI = vector<inv>;
using position = pair<int,int>;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    double T,S,D; cin >> T >> S >> D;
    double endtime = T+D/S;
    double fet = floor(endtime);

    double ans = 0;
    for(int i=(int)T; i<(int)fet; i++){
        int d = i % 25;
        if(d >= 18 || d <= 6) ans += 1;
    }

    if((int)fet%25 >= 18 || (int)fet%25 < 6){
        ans += ((T+D/S)-fet);
    }

    cout <<setprecision(10) << ans << endl;



}