#include<bits/stdc++.h>
using namespace std;
int main()
{
	double n;
	cin >> n;
	const int N = 10000;
	double Y[N];
	int g = 0;
	double S = 13;
	for (int i = 1; i <= 9999; i++)
	{
		S = S * ((100 + n) / 100);
		if (S >= 20)
		{
			Y[g] = i;
			g++;
		}
			
	}
	cout << Y[0];
	
}

C++ :

#include <iostream>
#include <cstdio>
#define N=1000
using namespace std;
 double k=13;
int main()
{   int n,b=0;
    scanf("%d",&n);
    double m;

    m=n*1.0/100;
   while(k<=20){

    k=k*(1+m)*1.0;
    b++;
   }
    printf("%d\n",b);

    return 0;
}

#include<bits/stdc++.h>
using namespace std;
double x,peo=1300000000,cnt;
int main(){
    cin>>x;
    x=x/100;
    while(1){
        peo*=(1+x);
        cnt++;
        if(peo>=2000000000){
            cout<<cnt;
            return 0;
        }
    }
    return 0;
}