Runtime error in Judge Online URI?

I can not figure out the runtime error for this program. The link to the question: link

#include <stdio.h>

int main()
{
int i,j,k,count,N,M[100];
char L[100];

while ((scanf("%d",&N))!=EOF)
    {for(i=0;i<N;i++)
        scanf("%d %c",&M[i],&L[i]);
    j=0;
    k=1;
    count=0;
    while(j<N)
        {for(i=k;i<N;i++)
            {if((M[j]==M[i])&&(L[j]!=L[i]))
                ++count;
            if((M[j]==M[i])&&(L[j]==L[i]))
                M[i]=0;
            }
        ++k;
        ++j;
        }
    printf("%d\n",count);
    }

return 0;
}