#include<bits/stdc++.h>

using namespace std;

int main()
{
	double n,m,t;//不改成double是否会出问题; 
	cin>>n>>m>>t;
	
	double l=0,r=1,keep=n,mid;//keep是每月应还;
	while(abs(l-r)>1e-3)
	{
		mid=(l+r)/2.0;
		while(t--)
		{
			keep=keep*(1+mid)-m;
		}
		if(abs(keep)>1e-3) r=mid;
		else l=mid;
	}
	printf("%.1lf",mid*100);
	return 0;
}