#include <iostream>
#include <vector>
#include <cstdlib>
struct vector_t: public std::vector<int> {
int& operator [] (unsigned int i){
if( this->size() <= i ){ this->resize(i+1); }
return this->at(i);
}
};
int main(){
using namespace std;
vector_t t;
int cnt, ten, i;
double sum, avg;
cnt = 0;
cin >> ten;
label_1:
if( ten != 999 ){
t[cnt] = ten;
cnt = cnt + 1;
cin >> ten;
goto label_1;
}
sum = 0;
i = 0;
label_2:
if( i < cnt ){
sum = sum + t[i];
i = i + 1;
goto label_2;
}
avg = sum / cnt;
cout << avg << endl;
exit(0);
}
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