C++ :

#include <bits/stdc++.h>
using namespace std;

int main(){
    double s, sum = 0, step = 2, cnt = 0;
    cin >> s;
    do {
        sum += step;
        cnt++;
        if (sum >= s) {
            break;
        }
        step *= 0.98;
    }while (true);
    cout << cnt;
    return 0;
}