Mirko has written the following function:

int fun() {
    int ret = 0;
    for (int a = X1; a <= Y1; ++a)
        for (int b = X2; b <= Y2; ++b)
            ...
                for (int <N-th> = XN; <N-th> <= YN; ++<N-th>)
                    ret = (ret + 1) % 1000000007;
    return ret;
}

function fun: longint;
var
    ret: longint;
    a, b, ... , y, z: longint;
begin
    ret := 0;
    for a := X1 to Y1 do
        for b := X2 to Y2 do
            ...
                for <N-th> := XN to YN do
                    ret := (ret + 1) mod 1000000007;
    fun := ret;
end;

<N-th> denotes the \(N\)th lowercase letter of the English alphabet. Each \(X_i\) and \(Y_i\) denotes either a positive integer less than or equal to \(100\,000\) or a name of a variable that some outer loop iterates over. For example, \(X_3\) can be either a, b, or an integer literal. At least one of \(X_i\) and \(Y_i\) will be an integer literal (i.e. not a variable name) for every \(i\).

Compute the return value of the function.

The first line of input contains the positive integer \(N\) (\(1 \le N \le 26\)).

For the next \(N\) lines, the \(i\)-th line contains \(X_i\) and \(Y_i\), separated with a space. If \(X_i\) and \(Y_i\) are both integer literals, then \(X_i \le Y_i\).

The first and only line of output must contain the return value of the function.

riseoj 작성

출처 COCI 2011/2012 Contest 2