#include<bits/stdc++.h>
#define ll long long
using namespace std;
int w0,w,m;
bool check(double x){
double left=w0;
for(int i=1;i<=m;i++){
left=left-(w-leftx);
}
if(left<=0)return 1;
else return 0;
}
int main(){
cin>>w0>>w>>m;
double l=0,r=3,mid=(l+r)/2;
while(abs(r-l)>0.00001){
mid=(l+r)/2;
if(check(mid))l=mid;
else r=mid;
}
printf("%.1lf%",mid100);
return 0;
}
