#include<stdio.h>
int main()
{
    int first_reactant, second_reactant;
    scanf("%d", &first_reactant);
    scanf("%d", &second_reactant);
    {
        printf("Invalid input.");
    }
    if(!= 2)
    {
        printf("Invalid input");
    }
    else if(first_reactant<0||second_reactant<0)
    {
        printf("Invalid input.");
    }
    else
    {
        int totalMass = first_reactant + second_reactant;
        printf("%d", totalMass);
    }
    return 0;
}