a, b, c, d = map(float, input().split())
aa = 2*d-c
bb = d*d/c
if a - b == b - c == c - d and aa == int(aa):
print(int(aa))
elif a / b == b / c == c / d and bb == int(bb):
print(int(bb))
else:
print(42)
#include <bits/stdc++.h>
#define IOS \
ios::sync_with_stdio(0); \
cin.tie(0); \
cout.tie(0);
#define ll long long
using namespace std;
int main(){
IOS
float a,b,c,d; cin >> a >> b >> c >> d;
if ((b-a)==(c-b) && (c-b)==(d-c))
cout << d+(b-a) << endl;
else if ((b/a)==(c/b) && (c/b)==(d/c)){
float r = d*(b/a);
cout << (r == (int)r ? r : 42) << endl;
}
else cout << 42 << endl;
return 0;
}1154A - Restoring Three Numbers | 750A - New Year and Hurry |
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