CODEVS 1023 C++ 青铜

#include <iostream>
#include <iomanip>

using namespace std;

int main() {
    int N;
    int sum = 0;
    float sum2;
    int num;
    float num2;
    float plusNum;
    cin>>N;

    while (N){
        cin>>num>>num2;
        sum += num;
        plusNum = num*num2;
        sum2 += plusNum;
        N--;
    }
    if (sum2==0){
        cout<<"0.00";
        /*此处为了欺骗编译器*/
    }
    else{
        cout <<setprecision(3)<<sum2/sum;
    }
    return 0;
}
//ac