C++

#include <iostream>
#include <vector>
using namespace std;

vector<int> fib;

int main()
{
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    fib.push_back(0), fib.push_back(1);
    while (fib.back() <= 1e8) {
        int b1 = fib[fib.size() - 1];
        int b2 = fib[fib.size() - 2];
        fib.push_back(b1 + b2);
    }
    int k; cin >> k;
    int dif = 0x3f3f3f3f;
    int res = -1;
    for (int i = 0; i < fib.size(); i++ ) {
        int cdif = abs(fib[i] - k);
        if (dif > cdif) {
            dif = cdif;
            res = fib[i];
        }
    }
    cout << res;
}