C++ :

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string a , b , r = "";
    cin >> a >> b;
    if(a == b)
    {
        cout << 0;
        return 0;
    }
    if(a.size() < b.size())
    {
        cout << "-";
        swap(a , b);
    }
    else if(a.size() == b.size() && a < b)
    {
        cout << "-";
        swap(a , b);
    }
    while(a.size() != b.size())
    {
        b = '0' + b;
    }
    int n = a.size() , x, y , f = 0;
    for(int i = n - 1;i >= 0;i--)
    {
        x = a[i];
        y = b[i];
        if(x - f - y < 0)
        {
            r =char( x - f + 10 - y + '0') + r;
            f = 1;
        }
        else
        {
            r = char(x - f - y + '0') + r;
            f = 0;
        }
    }
    while(r[0] == '0')
    {
        r.erase(0 , 1);
    }
    cout << r;
    return 0;
}

Python :

print(int(input())-int(input()))