x**n donne une liste, trouver n

var inputs = readline().split(' ');
let t = []
for (let i = 0; i < 15; i++) {
    const x = parseInt(inputs[i]);
    t.push(x)
}
let allZeros = (tab) => tab.reduce((a,b)=>a*1+b,0)==0
let etapes = 0
while(!allZeros(t))
{
    let tmp = []
    for(let i = 1; i < t.length; i++)
    {
        tmp.push(t[i] - t[i-1])
    }
    t = tmp
    etapes++
}
console.log(etapes-1)