#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define For(i,n,k) for(int i=(n);i<(k);i++)
#define ALL(a)  (a).begin(),(a).end()
ll ans = 0;
void Main(){
    double sx, sy, gx, gy;
    cin >> sx >> sy >> gx >> gy;
    sy = -sy;
    cout << fixed << setprecision(8) << sx - sy * (gx - sx) / (gy - sy) << endl;
}
int main(){
    Main();
    /*
    東方風神録は神が出てくるので当然神ゲー
    */
    return 0;
}
#include<bits/stdc++.h>
#define RT register
#define ll long long
#define ull unsigned long long
#define lowbit(x) (x&(-x))
using namespace std;

template<typename T>
inline void read(T &x){
    x=0; bool f=0;char ch=getchar();
    while(ch<'0'||ch>'9'){f|=ch=='-';ch=getchar();}
    while(ch>='0'&&ch<='9'){x=(x<<1)+(x<<3)+ch-'0';ch=getchar();}
    x=f?-x:x;
}
template<typename T>
inline void print(T x){
    if(x<0) x=-x,putchar('-');
    if(x>9) print(x/10);
    putchar(x%10+'0');
}
int x,y,z;

int main(){
    read(x),read(y),read(z);
    int m=y*z;
    if(m%x==0) print(m/x-1);
    else print(m/x);
    return 0;
}
