#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	int ans=0;
	double m=n;
	while(m<50){
		m*=1.1;
		ans++;
	}
	cout<<ans;
	return 0;
}

#include<cstdio>

int main(){
    int n;
    double ans;
    scanf("%d",&n);
    ans=n;
    for(int i=1;;i++){
        ans*=1.1;
        if(ans>=50){
            printf("%d\n",i);
            break;
        }
    }
    return 0;
}

//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;
}