#include <stdio.h>

int isPrime(int a);
int sum(int b);

int main()
{
    int n,m,a,b,c;
    int sumx;
	
    scanf("%d %d", &n, &m);
	
    a = sum(n);
    b = sum(m);
    c = isPrime(n);
    printf("%d\n",b-a+c);
} 
 
int isPrime(int a) 
{ 
    int x;
    int ret;
    int cnt=0;     
	
    for(x=1; cnt<200 ;x++)
    {
        int i;
    	int isPrime = 1;
    	for (i=2;i<x;i++)
	{
	    if (x%i==0)
	    {
	        isPrime=0;
	        break;
	    }
    		
	}
	if (isPrime == 1)
        {
	    if(cnt==a)
	    {
	        ret=x;
		goto out;	
	    }
	    else
	    {
	        cnt++;
	    }
	}
    }
out:
    return ret;
}

int sum(int b) 
{ 
    int x;
    int ret;
    int sum = 0;
    int cnt=0;
	
    for(x=2; cnt<200 ;x++)
    {
        int i;
    	int isPrime = 1;
    	for (i=2;i<x;i++)
        {
	    if (x%i==0)
            {
	        isPrime=0;
		break;
	    }
    		
	}
	if (isPrime == 1)
	{
	    cnt++;
	    sum += x;
	    if(cnt==b)
	    {
		ret=sum;
		goto out;
	    }
	}
    }
out:
    return ret;
}