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

int main(){
	int T,S,D;cin>>T>>S>>D;
	double ans=0;
	while(D>0){
		D-=S;
		if(D<0){
			ans+=(double)(D+S)/S;
			break;
		}
		ans+=(18<=T&&T<=23)|(0<=T&&T<=6);
		T=(T+1)%24;
	}
	cout<<fixed<<setprecision(15)<<ans<<endl;
}