Sum from a to b natural numbers Program

Sum from a to b natural numbers -

#include <stdio.h>

int main()
{ int a,b,i,s1=0,s2=0,s;
printf("Enter The numbers ");
  scanf("%d %d",&a,&b);
  for(i=1;i<b;i++)
  {s1=s1+i; }
  for(i=1;i<=a;i++)
  { s2=s2+i; }
  s=s1-s2 ;
printf("The sum is %d",s);
   return 0;
}

Output -

Enter the numbers 4
7
The sum is 11