#include using namespace std; int main(void) { int num; cin >> num; int ret = 0; switch (num % 5) { case 4: if (num / 5 < 1) {ret = -1; break;} else { ret = (num / 5) + 2; break; } case 3: ret = (num / 5) + 1; break; case 2: if (num / 5 < 2) { ret = -1; break; } else { ret = num / 5 + 2; break; } case 1: if (num / 5 < 1) { ret = -1; break; } else { ret = num / 5 + 1; break; } case 0: ret = num /..