#include <bits/stdc++.h>
using namespace std;
double check(int loan,int pay,int month,double rate){
    for(int i=0;i<month;i++){
        loan=loan*(1+rate)-pay;
    }
    return loan;
}
int main(){
    int loan,pay,month;
    double l=0,r=10,mid,t;
    cin>>loan>>pay>>month;
    while(l<=r){
        mid=(l+r)/2;
        if(r-l<0.0001){
            break;
        }
        t=check(loan,pay,month,mid);
        if(t==0){
            printf("%.1lf",mid*100);
            return 0;
        }else if(t>0){
            r=mid;
        }else{
            l=mid;
        }
    }
    printf("%.1lf",mid*100);
    return 0;
}