15815 천재 수학자 성필 문제풀이 #include #include using namespace std; void fast_io(void) { ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); } int main() { fast_io(); string str; stack s; cin >> str; int i = 0, res = 0; while (str[i] != '\0') { if (isdigit(str[i])) s.push(str[i] - 48); else { int b = s.top(); s.pop(); int a = s.top(); s.pop(); if (str[i] == '+') s.push(a + b..