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#include<bits/stdc++.h>
int main(){
    long long i,N,A,s[4]={1,0,0,0};
    scanf("%lld",&N);
    for(i=0;i<N;i++){
        scanf("%lld",&A);
        s[A]+=s[A-1];
    }
    printf("%lld\n",s[3]);
    return 0;
}
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