#include <stdio.h>

int main(void) {
	
	double a,r,T,S,oldS;
	
	a = 1,r = 0.9;
	T = a;
	S = a;
	
	do{
		oldS = S;
		T = T * r;
		S = oldS + T;
	}while((S - oldS) < 0.00001);
	
	printf("初項%f 項比%fの等比数列の和＝%f",a,r,S);
	
	return 0;
}