OJ Board

I keep getting Runtime error. Can someone please check.
#include <stdio.h>
main()
{
int f=1,ch,j,i,m,n;

scanf("%d %d ",&m,&n);
while ((m!=0)&&(n!=0))
{
char **st = new char*[m+1];
for (i=0;i<m+1;i++)
st[i] = new char[n];

char **st1 = new char*[m+3];
for (i=0;i<m+2;i++)
st1[i] = new char ...