#include <stdio.h>
#include <math.h>
void main()
{double b, a, n, i;
double S=0;
printf("\n VVedite a, b, n");
scanf_s("%lf%lf%lf",&a,&b,&n);
if (b>5) 
b=4;
if (a<2) 
a=2;
{for(i=1;i<=n;++i)
S+=pow(a*b,i-1)/i*(b-i);}
printf("\nS=%f\t",S);}