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#include <iostream>
#include <vector>
using namespace std;

bool is_A_smaller_than_B(string A, string B) {
    if(A.size() < B.size()) {
        return true;
    }
    if(A.size() > B.size()) {
        return false;
    }
    for(int i = 0; i < (int) A.size(); i++) {
        if(A[i] < B[i]) {
            return true;
        }
        if(A[i] > B[i]) {
            return false;
        }
    }
    return false;
}
string subtract_big_integer(string A, string B) {
    if(is_A_smaller_than_B(A, B)) {
        swap(A, B);
    }
    int sz_a = (int)A.size() - 1;
    int sz_b = (int)B.size() - 1;
    int carry = 0;
    string diff = "";
    while(sz_a >= 0 and sz_b >= 0) {
        int digit_a = (A[sz_a] - '0');
        int digit_b = (B[sz_b] - '0');
        int razlika = digit_a - digit_b - carry;
        if(razlika < 0) {
            razlika += 10;
            carry = 1;
        }
        else {
            carry = 0;
        }
        diff += (razlika + '0');
        sz_a--;
        sz_b--;
    }
    while(sz_a >= 0) {
        int digit_a = (A[sz_a] - '0');
        int razlika = digit_a - carry;
        if(razlika < 0) {
            carry = 1;
            razlika += 10;
        }
        else {
            carry = 0;
        }
        diff += (razlika + '0');
    }
    reverse(diff.begin(), diff.end());
    return diff;
}
int main()
{
    cout << subtract_big_integer("98421", "19999") << endl;

return 0;
}