#include <bits/stdc++.h>
using namespace std;
int dp[10010];
int solve(int H, const int A, const int D){
    if(H <= 0) return 0;
    if(dp[H]) return dp[H];
    int p1 = solve(H-A,A,D)+10;
    int p2 = solve(H-D,A,D)+15;
    return dp[H] = min(p1,p2);
}
int main(){
    int H,A,D;
    cin >> H >> A >> D;
    cout << solve(H,A,D)/10. << endl;
    return 0;
}