//这边建议徐老师去野外抓一只大黄蜂回来 
#include <bits/stdc++.h>
using namespace std;

//不用double（float）的等着废掉吧 
double n;
//认为徐老师不能在有生之年买到大黄蜂的用long long 
int year=0; 

int main(){
	scanf("%lf",&n);
	while(n<50.0){
		n*=1.1;
		year++;
	}
	printf("%d",year);
	return 0;
}