#include <stdio.h>

int main()
{
    int a,b,c,i;
    scanf("%d%d%d",&a,&b,&c);
    if(a>b)
    {
        i=a;
        a=b;
        b=i;
    }
    int length=b-a+1;
    if(c<=length)
    printf("%d",c+a+1);
    else
    {
        int q=(c-length+1)/2;
        printf("%d",c-q+a+1);
    }
    return 0;
}