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int array[110];
int n;
void init(int n) {
int i = 1;
while (i <= n * n + 1) {
array[i] = -1;
i = i + 1;
}
}
int findfa(int a) {
if (array[a] == a)
return a;
else {
array[a] = findfa(array[a]);
return array[a];
}
}
void mmerge(int a, int b) {
int m = findfa(a);
int n = findfa(b);
if (m != n) array[m] = n;
}
int main() {
int t, m;
int a, b;
t = 1;
while (t) {
t = t - 1;
n = 4;
m = 10;
int i = 0;
int flag = 0;
init(n);
int k = n * n + 1;
while (i < m) {
a = getint();
b = getint();
if (!flag) {
int loc = n * (a - 1) + b;
array[loc] = loc;
if (a == 1) {
array[0] = 0;
mmerge(loc, 0);
}
if (a == n) {
array[k] = k;
mmerge(loc, k);
}
if (b < n && array[loc + 1] != -1) {
mmerge(loc, loc + 1);
}
if (b > 1 && array[loc - 1] != -1) {
mmerge(loc, loc - 1);
}
if (a < n && array[loc + n] != -1) {
mmerge(loc, loc + n);
}
if (a > 1 && array[loc - n] != -1) {
mmerge(loc, loc - n);
}
if (array[0] != -1 && array[k] != -1 && findfa(0) == findfa(k)) {
flag = 1;
int tmp = i + 1;
putint(tmp);
putch(10);
}
}
i = i + 1;
}
if (!flag) {
putint(-1);
putch(10);
}
}
return 0;
}
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