#include <iostream>
#include <iomanip>

int main() {
    int n;
    std::cin >> n;

    // 拆分出百位、十位和个位
    int hundreds = n / 100;
    int tens = (n / 10) % 10;
    int units = n % 10;

    // 计算结果
    double result = static_cast<double>(hundreds + tens) / (tens + units);

    // 输出结果，保留两位小数
    std::cout << std::fixed << std::setprecision(2) << result << std::endl;

    return 0;
}
    
/**************************************************************
	Problem: 1608
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/