C++ :

#include <iostream>
using namespace std;

int main(){
	int c = 1;	
	double t = 2,s = 2,x;
	cin>>x;
	while(s < x){
		t = t * 0.98;
		s = s + t;
		c++;
	}
	
	cout<<c<<endl;
}

Python :

n = float(input())
i = 0
a = 2
b = 0
while(b < n):
    b += a
    a *= 0.98
    i += 1
print(i)