C++ :

#include <iostream>
using namespace std;
int main() {
    int num;
    int max_num = 0;
    bool flag = 0; // 标记第一个数
    do {
        cin >> num;
        if (flag==0){
            flag = 1;
            max_num = num;
        }
        if (num != -1 && num > max_num) {
            max_num = num;
        }
    } while (num != -1);
    cout << max_num;
    return 0;
}