CCC12 Mouse Journey

#include <iostream>

using namespace std;

int r,c;
int A[26][26];
bool B[26][26];
int k;

int main()
{
    cin>>r>>c;

    for (int i=0;i<r;i++)
        for (int j=0;j<c;j++)
        {
            A[i][j]=0;
            B[i][j]=true;
        }

    cin>>k;
    while (k--)
    {
        int r1,c1;
        cin>>r1>>c1;

        B[r1-1][c1-1]=false;
    }

    for (int i=0;i<c;i++)
        if (B[0][i]) A[0][i]=1;
        else break;

    for (int i=1;i<r;i++)
        if (B[i][0]) A[i][0]=1;
        else break;

    for (int i=1;i<r;i++)
        for (int j=1;j<c;j++)
            if (B[i][j]) A[i][j]=A[i-1][j]+A[i][j-1];

    cout<<A[r-1][c-1]<<endl;
    return 0;
}