idea

权重记得也是浮点数，否则2，5测试点不过

solution

#include <stdio.h>
int main(){
	int n ;
	double x0, ans = 0, power = 1;
	scanf("%d%lf", &n, &x0);
	double a[n+1];
	for(int i = 0; i <= n; i++)
		scanf("%lf", a + i);
	for(int i = n-1; i >= 0; i--){
		power *= x0;
		ans += a[i] * power;
	}
	printf("%.3f", ans + a[n]);
	return 0;
}