import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv, std.math,
    std.functional, std.numeric, std.range, std.stdio, std.string, std.random,
    std.typecons, std.container, std.format;

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
// dfmt on

void main()
{
    long N = lread();
    auto A = new long[](N);
    auto B = new long[](N);
    foreach (i; 0 .. N)
        scan(A[i], B[i]);

    long ans;
    foreach_reverse (i; 0 .. N)
    {
        long m = (A[i] + ans) % B[i];
        if (m == 0)
            continue;
        long d = B[i] - m;
        ans += d;
    }
    writeln(ans);
}
