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| #include <iostream>
#include <algorithm>
using namespace std;
int main() {
int n, x;
scanf("%d", &n);
int s1 = 0, s2 = 0, s3 = 0, s4 = 0;
while (n--) {
scanf("%d", &x);
if (x == 1) {
s1 = s1 + 1;
s3 = max(s3 + 1, s2 + 1);
} else {
s2 = max(s2 + 1, s1 + 1);
s4 = max(s4 + 1, s3 + 1);
}
}
printf("%d\n", max(s3, s4));
return 0;
}
|