错误代码(用函数真的多此一举了orz)：

#include<iostream>

using namespace std;

int n, k;
double s(int x) {
    double sum=0;
    for (int i=1;i<=x;i++)
    {
        sum += 1.0/i;
    }
    return sum;
}

int main() {
    cin >> k;
    n = k;
    while (s(n) <= k)
    {
        n++;
    }
    cout << n;
    return 0;
}

AC代码：

#include <iostream>

using namespace std;

int main(){
    double k;
    cin >> k;

    double sum = 0;
    for (double i = 1;; i ++){
        sum += 1 / i;
        if (sum > k){
            cout << i << endl;
            break;
        }
    }

    return 0;
}

数论（调和级数）：

#include<iostream>
#include<cmath>
const double gamma=0.5772156649;
int main() {
    int k,n;
    cin>>k;
    n=exp(k-gamma)+0.5;
    cout<<n;
    return 0;
}