    #include <bits/stdc++.h>
    
             
    #define IOS         ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
    typedef long long      ll;
    #define rep(i,n)     for(int i=0;i<n;i++)
    #define gcd(a,b)       __gcd(a,b)
    #define lcm(a,b)	(a*b)/gcd(a,b)
    #define mem1(a)        memset(a,-1,sizeof(a))
	#define mem0(a)        memset(a,0,sizeof(a))
    #define vint        vector<int>
    #define pb            push_back
    #define pf            push_front
    #define ppb         pop_back
    #define all(v)      v.begin(),v.end()
    #define pii         pair<int,int>
    #define pic         pair<int,char>
    #define fr            first
    #define sc         second
    #define mp         make_pair
    #define inarr(a,n)	for(ll i=0;i<n;i++)cin>>a[i]; 
    #define PI   		3.1415926535897
    #define time_passed	1.0 * clock() / CLOCKS_PER_SEC
    using namespace std;
     
    double power(double a,int b) {if(b==0){return 1;}else if(b%2==0){return power(a*a,b/2);}else if(b%2==1){return a*power(a*a,(b-1)/2);}}
	//bool cmp(a[l] , a[r]){return b[1][l]<b[1][r];}
	template<typename T1,typename T2>istream& operator>>(istream& in,pair<T1,T2> &a){in>>a.x>>a.y;return in;}
	template<typename T1,typename T2>ostream& operator<<(ostream& out,pair<T1,T2> a){out<<a.x<<" "<<a.y;return out;}
	template<typename T,typename T1>T maxs(T &a,T1 b){if(b>a)a=b;return a;}
	template<typename T,typename T1>T mins(T &a,T1 b){if(b<a)a=b;return a;}
 	
 	double f(double x,double Nu,double k){return power(x,k)-Nu;}
	double fd(double x,double Nu,double k){return k*pow(x,k-1);}
	double root(int Nu,int k){double ans=9;for(int i=1;i<20;i++){ans=ans-f(ans,Nu,k)/fd(ans,Nu,k);cout<<ans<<" ";}return ans;}
	
	
	
	const ll mod=power(2,32);
	const int N=3e5+5;
	const ll inf=1e9+7;
 	int dy[]={-1,0,1,0};
 	int dx[]={0,1,0,-1};
 	vector <int >adj[N];
 	//int vis[201][201];
 	//int  dist[N];
 	
	
	
	
    void love_for_infinity()
    {
    	float a,b,c,d;
    	cin>>a>>b>>c>>d;
    	cout<<fixed<<(b*(c-a)/(d+b))+a<<setprecision(9);
    
    
	}
    
    
    
    int main()
    {    IOS
    	//freopen("input.txt", "r", stdin);
	    //freopen("output.txt", "w", stdout);
	    #ifdef SIEVE
	    sieve();
	    #endif
	    #ifdef NCR
	    init();
	    #endif
        ll t;t=1;//cin>>t;
        while(t--){love_for_infinity();cout<<endl;}
        return 0;
    }
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define forn(i,x,n) for(int i = x;i <= n;++i)
#define forr(i,x,n) for(int i = n;i >= x;--i)
#define Angel_Dust ios::sync_with_stdio(0);cin.tie(0)


int main()
{
    int a,b;scanf("%d%d",&a,&b);
    printf("%.18lf\n",a * b / 100.0);
    return 0;
}   
