#include<stdio.h>
main()
{long n,m,a,b,p;
   scanf("%d %d",&n,&m);
      p=sum(n,m);
        printf("The sum from %d to %d is %d\n",n,m,p);
}
sum(long n,long m)
 {
   if(n==m) return(n);
     else
      return(n+sum(n-1,m));
 }
错哪了呢？

高手，还是过不去呀