wht am i missing here?

#include<stdio.h>

int main()
{
    int th,co,n1,n2,z;
    long s;
    scanf("%d %d %d %d",&th,&co,&n1,&n2);
    if(n2>n1)
    {
        z=n2-n1;
        s=2*z*co+((z-1)*th);
    }
    else
    {
        z=n1-n2;
        s=((2*z)+1)*co+(z+1)*th-1;
    }
    printf("%ld\n",s);
    return 0;
}

Please tell me why WA5

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