#include<stdio.h> bool chk[3]; int R; void Move(){ if (chk[2])R++; chk[2] = chk[1]; chk[1] = chk[0]; chk[0] = false; } int main(){ int i, n, a, B = 0; scanf("%d", &n); while (n--){ scanf("%d", &a); if (a == 1){ if (B == 3){ Move(); B = 0; chk[0] = true; } else B++; continue; } else if (a == 2){ B = 0; Move(); chk[0] = true; } else{ Move(); B++; if (B == 4){ chk[0] = true; B = 0; } } } printf("%d\n", R); }