/*
 *Student: S.K Soekhlal
 * Number: 4860632
 * Assignment: 1.4
 */

#include<stdio.h>
#include<stdlib.h>
#include<math.h>

int main(){
    double a,r,b=0,sum=0; /*Declaring variables*/
    int N;
    scanf("%lf%d%lf",&a,&N,&r); /*Storing inputted values in variables*/
    for(;N>=0;--N){         /*Starting for loop to calculate sum*/
        b = a * (pow(r,N)); /*calculating sum*/
        sum += b;
    }
    printf("%.2f\n", sum);  /*Printing sum on the screen*/
    return 0;
}