std::getline和std::vector的怪异行为<std::string>

我有以下代码:

std::vector<std::string> final_output;
std::string input;

int tries = 0;
std::cin >> tries;

int counter = 0;
while(counter < tries) {

    std::getline(std::cin, input); 
    final_output.push_back(input);
    ++counter;

}

给定输入:

3
Here Goes
Here Goes 2

输出为:

<blank line>
Here Goes
Here Goes 2

但是,如果我的代码是:

int tries = 3;         // explicitly specifying the number of tries
int counter = 0;
while(counter < tries) {}

它按预期工作。为什么 std::cin >> tries 导致代码失败?