What does this C++ snippet output?

1#include <iostream>
2#include <vector>
3#include <algorithm>
4int main() {
5    std::vector<int> v = {1, 2, 3, 4, 5, 6};
6    int evens = std::count_if(v.begin(), v.end(), [](int x){ return x % 2 == 0; });
7    std::cout << evens << "\n";
8}