int iterations;

for(int o=0;o<iterations;o++)

{

int number,number1,i,j,min=0,max=0,count=0;

scanf("%d",&number1);

scanf("%d",&number);

// scanf("%d",&number1);

int primes[number+1];

//populating array with naturals numbers

for(i = 2; i<=number; i++)

primes[i] = i;

i = 2;

while ((i*i) <= number)

{

if (primes[i] != 0)

{

for(j=2; j<number; j++)

{

if (primes[i]*j > number)

break;

else

// Instead of deleteing , making elemnets 0

primes[primes[i]*j]=0;

}

}

i++;

}

for(int m=number1;m<=number;m++)

{

if(primes[m]!=0)

{

count++;

if(min==0)

min=primes[m];

if(m>max)

max=primes[m];

}

}

if(count==0)

printf("%d",-1);

if(count>0)

{

printf("%d\n",max-min);

}

}