#include<iostream>
#include<iomanip>
using namespace std;

int main(d){
double all,pay,m,ans,L=0,R=10,mid;
cin>>all>>pay>>m;
while(R-L>1e5-5){
	double t=all;
	mid=(L+R)/2;
	for(int i=1;i<=m;i++){
		t=t*(1+mid)-pay;
	}
	if(t>0){
		R=mid-0.0001;
	}
	else{
		L=mid+0.0001;
	}
}
cout<<fixed<<setprecision(1)<<mid*100;
   return 0;
}