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- for(i=0; i<5; i++)
- sum += factorial(p-i) % p;
- ll powmod(ll a, ll b){//a^b % MOD
- ll x=1,y=a;
- while(b){
- if(b&1){
- x*=y; if(x>=MOD)x%=MOD;
- }
- y*=y; if(y>=MOD)y%=MOD;
- b>>=1;
- }
- return x;
- }
- ll InverseEuler(ll n){//modular inverse of n
- return powmod(n,MOD-2);
- }
- ll factMOD(ll n){ //n! % MOD efficient when MOD-n<n
- ll res=1,i;
- for(i=1; i<MOD-n; i++){
- res*=i;
- if(res>=MOD)res%=MOD;
- }
- res=InverseEuler(res);
- if(!(n&1))
- res= -res +MOD;
- }
- return res%MOD;
- }
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