一本通1639：Biorhythms

#include <cstdio>
using namespace std;
int D, x, y, M = 21252, num;
int a[3], m[3] = {23, 28, 33}, inv;

int exgcd(int a, int b, int &x, int &y) {
    if (!b) {
        x = 1;
        y = 0;
        return a;
    }

    int t = exgcd(b, a % b, x, y);
    long long tmp = x;
    x = y;
    y = tmp - a / b * y;
    return t;
}

int main() {
    while (1) {
        num += 1;
        x = 0;
        scanf("%d%d%d%d", &a[0], &a[1], &a[2], &D);

        if (a[0] == -1 and a[1] == -1 and a[2] == -1 and D == -1)
            break;

        for (int i = 0; i < 3; i += 1) {
            exgcd(M / m[i], m[i], inv, y);
            x = (x + 1ll * M / m[i] * a[i] * inv) % M;
        }

        if (x <= D)
            x += M;

        printf("Case %d: the next triple peak occurs in %d days.\n", num, x - D);
    }

    return 0;
}