/* 输入12行浮点数,计算平均数,保留2位小数*/

#include <stdio.h>

#define MONTH 12

int main(void)
{
    int month = MONTH;
    float balance, tmp = 0;
    while(month--)
    {
        scanf("%f", &balance);
        tmp += balance;
    }

    printf("$%.2f\n", tmp / MONTH);
    return 0;
}