#include<iostream>
#include<string>
using namespace std;
class Emp{
    double th =0, tt=0;
    public:
    void add(int h,int t){th +=h;tt+=t;}
    double getAvg {return tt/th;}
    static void show(double v){cout <<v;}
};
int main(){
    string id;int n,h,t;
    getline(cin,id);
    if(!(cin>>n)||n<1||n>10)return cout <<"Invalid input",0;
    Emp e;
    while(n--){
        if(!(cin>>h>>t)||h<1||h>24||t<0||100)
        return cout<<"Invalid input",0;
        e.add(h,t);
    }
    Emp::show(e.getAvg());
    return 0;
}