framework: https://github.com/chu-mirror/probs

@[main@]
{ int c1, c2, c3, s, n=0;
	while (scanf("%d%d%d%d", &c1, &c2, &c3, &s), c1 != -1 && c2 != -1 && c3 != -1 && s != -1) { int f;
		@{compute f from c1, c2, c3@}
		printf("Case %d: the next triple peak occurs in %d days.\n", ++n, f - s);
	}
}
@

@[compute f from c1, c2, c3@]
{ int n1, n2, m;
	@{compute n1 from c1, c2@}
	@{compute n2 from c1, c3@}
	@{compute m from n1, n2@}
	f = c1 + 23 * (n1 + 28 * m);
	f = MOD(f, (23 * 28 * 33));
	if (f-s <= 0) f += 23 * 28 * 33;
}
@

@[compute n1 from c1, c2@]
{ int n, c;
	extended_gcd(23, 28, &n1, &n, &c);
	n1 *= c2 - c1;
}
@

@[compute n2 from c1, c3@]
{ int n, c;
	extended_gcd(23, 33, &n2, &n, &c);
	n2 *= c3 - c1;
}
@

@[compute m from n1, n2@]
{ int n, c;
	extended_gcd(28, 33, &m, &n, &c);
	m *= n2 - n1;
}
@

@[samples@]
===
0 0 0 0
0 0 0 100
5 20 34 325
4 5 6 7
283 102 23 320
203 301 203 40
-1 -1 -1 -1
>>>
Case 1: the next triple peak occurs in 21252 days.
Case 2: the next triple peak occurs in 21152 days.
Case 3: the next triple peak occurs in 19575 days.
Case 4: the next triple peak occurs in 16994 days.
Case 5: the next triple peak occurs in 8910 days.
Case 6: the next triple peak occurs in 10789 days.
@