Fibonacci number calculating code giving inconsistent anwers

Question

I have made a code for computing nth Fibonacci number's mod m ie Fn%m but this code gives correct answers sometimes and incorrest in other cases. one particular case where the answer comes out to be incorrect is when n=1000 and m=100 where the actual answer is 75 and this code gives 71. Can anyone help me out?

#include <iostream>
#include<vector>
#define ull unsigned long long
ull fibmod(ull n, ull m) 
{
    ull temp,prev=0,curr=1,pp;
    for(int i=0;i<=m*m;i++)
    {
        temp=prev;
        prev=curr;
        curr=(temp+curr)%m;
        std::cout<<curr<<" ";
        if(prev==0&&curr==1)
        {    
            pp=i+1;
            break;
        }
    }
    n=n%pp;
    //std::cout<<pp<<" "<<n<<"\n";
    prev=0;
    curr=1;
    if(n==0)
        return(0);
    else if(n==1)
        return(1);
    else
    {
        for(int i=0;i<n-1;i++)
        {
            temp=prev;
            prev=curr;
            curr=temp+curr;
        }
        return(curr%m);
    }
}
int main() {
    unsigned long long n, m;
    std::cin >> n >> m;
    std::cout << fibmod(n, m) << "\n";
}