Your program is write up to if(m==n)

in the above program n will become zero
after the loop. So assign n value to any other variable,then compare with m.

void main()
{int n=1,i=0;
clrscr();
while(i<1500)
{ n++;
if(n%2==0||n%3==0||n%5==0)
i++;

}
printf("%d",n);